Move to Micrometer's `Observations` API

[odrotbohm]

Our current observability integration is implemented against Micrometer's tracing APIs. We should rather move to the Observations API so that we can produce improved observations including metrics about module invocations, published and received events etc.

Related issues

• ObservedModule should be able to detect whether a MethodInvocation is an event listener invocation #927

[odrotbohm]

That's polished and merged! 🙇