[BUG] UnsupportedOperationException when building nativeHeaders

[moarychan]

Describe the bug
The UnsupportedOperationException will be encountered when azure-spring-cloud-stream-binder-eventhubs and spring-cloud-starter-sleuth are used together.
The PR microsoft/spring-cloud-azure#743 and microsoft/spring-cloud-azure#744 were to fix the issue microsoft/spring-cloud-azure#592. At that time, the properties of the EventData could still be modified, this PR #22314 changed properties to an unmodifiable Map, then a mistake was made without sufficient testing during version upgrade.

Exception or Stack Trace

com.azure.messaging.eventhubs.implementation.PartitionProcessorException: Error in event processing callback
	at com.azure.messaging.eventhubs.PartitionPumpManager.processEvents(PartitionPumpManager.java:322) ~[azure-messaging-eventhubs-5.10.1.jar:5.10.1]
	at com.azure.messaging.eventhubs.PartitionPumpManager.lambda$startPartitionPump$2(PartitionPumpManager.java:235) ~[azure-messaging-eventhubs-5.10.1.jar:5.10.1]
	at reactor.core.publisher.LambdaSubscriber.onNext(LambdaSubscriber.java:160) ~[reactor-core-3.4.9.jar:3.4.9]
	at reactor.core.publisher.FluxPublishOn$PublishOnSubscriber.runAsync(FluxPublishOn.java:440) ~[reactor-core-3.4.9.jar:3.4.9]
	at reactor.core.publisher.FluxPublishOn$PublishOnSubscriber.run(FluxPublishOn.java:527) ~[reactor-core-3.4.9.jar:3.4.9]
	at org.springframework.cloud.sleuth.instrument.reactor.ReactorSleuth.lambda$null$6(ReactorSleuth.java:309) ~[spring-cloud-sleuth-instrumentation-3.0.3.jar:3.0.3]
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:84) ~[reactor-core-3.4.9.jar:3.4.9]
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:37) ~[reactor-core-3.4.9.jar:3.4.9]
	at java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264) ~[na:na]
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java) ~[na:na]
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304) ~[na:na]
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
	at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]
Caused by: com.azure.messaging.eventhubs.implementation.PartitionProcessorException: Error in event processing callback
	at com.azure.messaging.eventhubs.PartitionPumpManager.processEvent(PartitionPumpManager.java:284) ~[azure-messaging-eventhubs-5.10.1.jar:5.10.1]
	at com.azure.messaging.eventhubs.PartitionPumpManager.processEvents(PartitionPumpManager.java:318) ~[azure-messaging-eventhubs-5.10.1.jar:5.10.1]
	... 13 common frames omitted
Caused by: java.lang.UnsupportedOperationException: null
	at java.base/java.util.Collections$UnmodifiableMap.remove(Collections.java:1460) ~[na:na]
	at com.azure.spring.integration.eventhub.converter.EventHubMessageConverter.buildCustomHeaders(EventHubMessageConverter.java:80) ~[azure-spring-integration-eventhubs-2.9.0.jar:2.9.0]
	at com.azure.spring.integration.eventhub.converter.EventHubMessageConverter.buildCustomHeaders(EventHubMessageConverter.java:30) ~[azure-spring-integration-eventhubs-2.9.0.jar:2.9.0]
	at com.azure.spring.integration.core.converter.AbstractAzureMessageConverter.toMessage(AbstractAzureMessageConverter.java:83) ~[azure-spring-integration-core-2.9.0.jar:2.9.0]
	at com.azure.spring.integration.eventhub.impl.EventHubProcessor.onEvent(EventHubProcessor.java:74) ~[azure-spring-integration-eventhubs-2.9.0.jar:2.9.0]
	at com.azure.messaging.eventhubs.EventProcessorClientBuilder$1.processEvent(EventProcessorClientBuilder.java:595) ~[azure-messaging-eventhubs-5.10.1.jar:5.10.1]
	at com.azure.messaging.eventhubs.PartitionPumpManager.processEvent(PartitionPumpManager.java:274) ~[azure-messaging-eventhubs-5.10.1.jar:5.10.1]
	... 14 common frames omitted

To Reproduce

• Use this sample;
• Replace the dependencyManagement and dependencies as following:

<dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-dependencies</artifactId>
        <version>2020.0.3</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
      <dependency>
        <groupId>com.azure</groupId>
        <artifactId>azure-core</artifactId>
        <version>1.20.0</version>
      </dependency>
    </dependencies>
  </dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
      <groupId>com.azure.spring</groupId>
      <artifactId>azure-spring-cloud-stream-binder-eventhubs</artifactId>
      <version>2.9.0</version>
    </dependency>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-logging</artifactId>
    </dependency>
    <dependency>
      <groupId>org.hibernate.validator</groupId>
      <artifactId>hibernate-validator</artifactId>
    </dependency>
    <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-starter-sleuth</artifactId>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
    </dependency>
  </dependencies>

• Send message, curl -X POST http://localhost:8080/messages/imperative/staticalDestination?message=hello

Code Snippet

@Override
    protected Map<String, Object> buildCustomHeaders(EventData azureMessage) {
        Map<String, Object> headers = super.buildCustomHeaders(azureMessage);

        headers.putAll(getSystemProperties(azureMessage));

        Map<String, Object> properties = azureMessage.getProperties();
        if (properties.containsKey(NATIVE_HEADERS) && isValidJson(properties.get(NATIVE_HEADERS))) {
            String nativeHeader = (String) properties.remove(NATIVE_HEADERS);
            properties.put(NATIVE_HEADERS, readValue(nativeHeader, LinkedMultiValueMap.class));
        }
        headers.putAll(azureMessage.getProperties());
        return headers;
    }
```

**Expected behavior**
No exceptions and better the tracing information transfers normally.

**Setup (please complete the following information):**
 - OS: Windows
 - IDE: IntelliJ
 - Library/Libraries: com.azure.spring:azure-spring-cloud-stream-binder-eventhubs:2.9.0
 - Java version: 11
 - Frameworks: org.springframework.boot:spring-boot-starter-parent:2.5.4, org.springframework.cloud:spring-cloud-dependencies:2020.0.3

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