* Add documentation for Observability
* Adapt Observation code to the latest dependencies
* Add doc generation tasks for meters and spans
* Document new Observation API features
* Include generated meters and spans docs to a general `metrics.adoc` chapter
* * Adapt `ObservationPropagationChannelInterceptorTests` for the latest `SpansAssert` API
* * Adjust to the latest Micrometer SNAPSHOT
* Make Observation doc generation tasks only as local.
We don't need ambiguous changes to source code on CI
* * Automate metrics/spans docs generation as a part of `reference` build phase
* Replace 'org.springframework.integration' content in the generated files with a 'o.s.i'
to make it easier to read, especially in the tables
* Break `DefaultMessageReceiverObservationConvention <=> IntegrationObservation` classes tangle
using literal for `KeyValues` in the `DefaultMessageReceiverObservationConvention`
instead of nested enums from the `IntegrationObservation`
* Some other minor build script clean up
* Fix indent in `build.gradle` for `micrometerVersion` property code line
* Add new line after observation section in whats-new.adoc
* * Adapt to the latest Micrometer changes
* * Use Reactor `2022.0.0-SNAPSHOT` version
f24fbd992b