This commit also updates tests since UNDERTOW-1260 has been fixed in
this release.

Closes gh-12852

As pointed out by Rossen in gh-11514 comments, a handler might commit
the response and then send an error signal in the pipeline. In this
case, adding a callback to `beforeCommit` is useless because it won't be
triggered. In those cases, we need to collect metrics right away.

See gh-10790

This commits make sure that the Quartz auto-configuration no longer
associates an `Executor` bean if present in the context as Quartz offers
properties to tune it, which would mutate and lead to unexpected
results.

Closes gh-12823

Spring Boot now deploys both annotation-based and functional endpoints
under the same `HttpHandler`; this means the currently auto-configured
`MetricsWebFilter` is instrumenting all endpoints to produce metrics.

There is no need for a WebFlux functional specific support.
This commit removes mentions of `RouterFunctionMetrics` in the docs and
deprecates that class.

Closes gh-12833

Prior to this commit, the metrics `WebFilter` would handle exceptions
flowing through the pipeline and extract tag information right away.
Since error handling turns the exception information into error HTTP
responses later in the chain, the information extracted from the
response earlier is invalid.
In this case, the "status" information could be "200" whereas error
handlers would later set that status to "500".

This commit delays the tags extraction later in the process, right
before the response is comitted. The happy path is not changed, as
handlers signal that the response is fully taken care of at that point.

Fixes gh-11514

* pr/12842:
  Fix WebClient example constructor name

Closes gh-12842

See gh-10790

Closes gh-12821

Closes gh-12827

* pr/12825:
  Fix typo

Closes gh-12825

Fixes gh-10851

Previously to this commit, if a `@ControllerEndpoint`,
`@RestControllerEndpoint` or `@ServletEndpoint` annotated bean was
proxied, the endpoint wasn't properly detected.

This commit makes sure that annotation retrieval works on the user class
while preserving the get (vs. find) retrieval semantic

Closes gh-12441

* pr/12812:
  Polish contribution
  Polish

Closes gh-12812

See gh-12812

Closes gh-12815

Closes gh-12806

Closes gh-12796