Add support for Micrometer tracing

[mhalbritter]

Implements auto-configurations for Micrometer Tracing

See gh-30156

So far this auto-configuration supports:

• Zipkin with a configurable URL, using JSON_V2 encoding and HTTP transport
• Wavefront with a configurable URL
• Configurable sampling probability (0% - 100%) for Brave and for OpenTelemetry
• Brave configured for Zipkin
• Brave propagation with B3 headers
• OpenTelemetry configured for Zipkin
• Micrometer tracing bridges for Brave and OpenTelemetry
• Micrometer observation handler for tracing
• Brave configured for Wavefront
• OpenTelemetry configured for Wavefront

[wilkinsona]

Thanks, Mortiz. I've left a few comments for your consideration.

Could you also double-check that any new packages that are introduced have package-info.java files.

[mhalbritter]

These are the dependency combinations i have tested with and which produce spans in backends:

Zipkin & Brave (no spring-web)

	implementation 'org.springframework.boot:spring-boot-starter-actuator'
	implementation 'io.micrometer:micrometer-tracing-bridge-brave'
	implementation 'io.zipkin.reporter2:zipkin-sender-urlconnection'


Zipkin & Brave (RestTemplate)

	implementation 'org.springframework.boot:spring-boot-starter-actuator'	
	implementation 'io.micrometer:micrometer-tracing-bridge-brave'
	implementation 'org.springframework.boot:spring-boot-starter-web'

Zipkin & Otel (no spring-web)

	implementation 'org.springframework.boot:spring-boot-starter-actuator'
	implementation 'io.micrometer:micrometer-tracing-bridge-otel'
	implementation 'io.zipkin.reporter2:zipkin-sender-urlconnection'
	implementation 'io.opentelemetry:opentelemetry-exporter-zipkin'

Zipkin & Otel (RestTemplate)

	implementation 'org.springframework.boot:spring-boot-starter-actuator'
	implementation 'io.micrometer:micrometer-tracing-bridge-otel'
	implementation 'org.springframework.boot:spring-boot-starter-web'
	implementation 'io.opentelemetry:opentelemetry-exporter-zipkin'

Wavefront & Otel

	implementation 'org.springframework.boot:spring-boot-starter-actuator'
	implementation 'io.micrometer:micrometer-tracing-bridge-otel'
	implementation 'io.micrometer:micrometer-tracing-reporter-wavefront'

Wavefront & Brave

	implementation 'org.springframework.boot:spring-boot-starter-actuator'
	implementation 'io.micrometer:micrometer-tracing-bridge-brave'
	implementation 'io.micrometer:micrometer-tracing-reporter-wavefront'

For Wavefront, at least the management.wavefront.api-token must be set, otherwise startup fails:

Caused by: org.springframework.boot.context.properties.source.InvalidConfigurationPropertyValueException: Property management.wavefront.api-token with value 'null' is invalid: This property is mandatory whenever publishing directly to the Wavefront API
	at org.springframework.boot.actuate.autoconfigure.wavefront.WavefrontProperties.getApiTokenOrThrow(WavefrontProperties.java:125) ~[classes/:na]
	at org.springframework.boot.actuate.autoconfigure.wavefront.WavefrontAutoConfiguration.wavefrontSender(WavefrontAutoConfiguration.java:51) ~[classes/:na]
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[na:na]
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
	at java.base/java.lang.reflect.Method.invoke(Method.java:568) ~[na:na]
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:130) ~[spring-beans-6.0.0-M3.jar:6.0.0-M3]
	... 140 common frames omitted

[wilkinsona]

This looks great, thank you. Particular thanks for testing the auto-configurations so thoroughly.

I've left a few comments, almost entirely minor and trivial polishing. The one thing that I think requires some further thought is around the use of spring.application.name. Please take a look and see what you think. My feeling is that we should create a separate issue and review things more broadly as it affects more than this new tracing support.

[mhalbritter]

Blocked on micrometer-metrics/tracing#16

[mhalbritter]

Rebased and put into main, see 3860eb2