* Add some infrastructure for Observation
* Populate an `ObservationRegistry` bean from the `IntegrationManagementConfigurer`
into all the `IntegrationManagement` components
* Introduce `MessageReceiverContext` and `MessageSenderContext` for easier usage
in the target code
* Implement `Observation` handling in the `AbstractMessageHandler`
* Modify `ObservationPropagationChannelInterceptorTests` for new `MessageSenderContext`
* Use `BridgeHandler` to ensure that `Observation` is propagated and handled properly
* Verify that tags from the `AbstractMessageHandler` are preset on the consumer span
* * Add a `DocumentedObservation` infrastructure
* * Add `Timer` verification to the propagation test
* * Update to the latest Observation API
* * Add custom observation convention support for the `AbstractMessageHandler`
* Use more meaningful prefix for Spring Integration tags
* * Move singleton instance for `DefaultMessageReceiverObservationConvention`
into `DefaultMessageReceiverObservationConvention` per se as an `INSTANCE` constant
* Use `MeterRegistryAssert` in the `ObservationPropagationChannelInterceptorTests`
to verify meters emitted
* * And an integration test with Zipkin based on the `SampleTestRunner`
8c73a2d0cd