Sql aggregator does not work in native mode, solve DefaultExchangeHolder globally.

[JiriOndrusek]

During fixation of #2623, I found an issue with sql aggregator in native mode.

Firstly, simple Caused by: java.lang.ClassNotFoundException: org.apache.camel.support.DefaultExchangeHolder is thrown.
Fix (by addition of ReflectiveClassBuildItem) uncovers more serious issue. Problem is happening during serialization/deserialization of DefaultExchangeHolder.

Caused by: com.oracle.svm.core.jdk.UnsupportedFeatureError: The offset of private java.lang.Exception org.apache.camel.support.DefaultExchangeHolder.exception is accessed without the field being first registered as unsafe accessed. Please register the field as unsafe accessed. You can do so with a reflection configuration that contains an entry for the field with the attribute "allowUnsafeAccess": true. Such a configuration file can be generated for you. Read BuildConfiguration.md and Reflection.md for details.
	at com.oracle.svm.core.util.VMError.unsupportedFeature(VMError.java:87)
	at jdk.internal.misc.Unsafe.objectFieldOffset(Unsafe.java:50)
	at java.io.ObjectStreamClass$FieldReflector.<init>(ObjectStreamClass.java:2002)
	at java.io.ObjectStreamClass.getReflector(ObjectStreamClass.java:2266)
	at java.io.ObjectStreamClass.<init>(ObjectStreamClass.java:534)
	at java.io.ObjectStreamClass.lookup(ObjectStreamClass.java:381)
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1135)
	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:349)
	at org.apache.camel.processor.aggregate.jdbc.JdbcCamelCodec.encode(JdbcCamelCodec.java:98)

I've tried suggested solution and I've also tried to register class for serialization (using native approach oracle/graal#2730), but it didn't help.

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Problem is solvable with native serialization. But for such a solution it would be nice to register DefaultExchangeHolder and linked types in some core module.

[JiriOndrusek]

Enable test from #2694, which is covering this issue.