Closes gh-22838

Closes gh-22850

Closes gh-22849

* pr/21615:
  Polish "Migrate legacy endpoint that have a dash in their id"
  Migrate legacy endpoint that have a dash in their id

Closes gh-21615

See gh-21615

See gh-21615

* pr/22839:
  Fix some doc anchors

Closes gh-22839

See gh-22839

Closes gh-22848

Closes gh-22847

* pr/22777:
  Polish "Propagate the cause that led Reactor"s debug agent to fail"
  Propagate the cause that led Reactor"s debug agent to fail

Closes gh-22777

See gh-22777

Prior to this commit, DebugAgentEnvironmentPostProcessor throws a
RuntimeException with a generic error message if its initialization
fails. The causing exception is discarded, which makes error analysis
unnecessarily difficult.

This commit attaches the cause to the newly thrown RuntimeException.

See gh-22777

Closes gh-22841

Closes gh-22846

* pr/22760:
  Fix wrong reference in `ReadinessStateHealthIndicator` javadoc

Closes gh-22760

See gh-22760

See gh-22844

See gh-22843

See gh-22842

See gh-22841

See gh-22729

This commit updates our usage of `MonoProcessor` after the deprecations
introduced in reactor/reactor-core#1053

Fixes gh-22776

Closes gh-22831

Previously, the Maven plugin integration tests used a settings.xml file
that defined https://repo.spring.io/snapshot as a repository. This
allowed them to resolve snapshots of the plugin's Spring Framework
dependencies but it had the unfortunate side-effect of also allowing
them to resolve snapshots of other Spring Boot modules from Artifactory
rather than using those currently being built.

This commit replaces the repositories in settings.xml with a Gradle
task that resolves the necessary dependencies and populates a local
repository with the dependencies' jars and pom files. This is achieved
using a ComponentMetadataRule that creates a custom variant of each
dependency that includes its pom file, inspired by the example in
gradle/gradle/#11449. A configuration that extends the
runtimeClasspath configuration and select the custom variant via its
attribute is then used to resolve the jars and pom files of the runtime
classpath such that they can then be used to populate the local
repository.

Closes gh-22828

Closes gh-22826

Prior to this commit, the HTTP/2 server auto-configuration for Jetty
would require Conscrypt as a hard dependency.

This commit updates the auto-configuration for more flexibility and now
allows the following deployments:

* JDK9+ with the JDK ALPN implementation
* JDK8u252+ with the backported ALPN implementation
* Conscrypt with no JDK requirement

The auto-configuration now improves detection and guides developers in
case there is a missing `jetty-alpn-*-server` dependency.

The reference docs in the HOWTO section has been updated accordingly.

Closes gh-22188

Closes gh-22820

Closes gh-22819

Closes gh-22818

Closes gh-22817

Closes gh-22816

Closes gh-22815

Closes gh-22814