Closes gh-21147

Closes gh-21146

Closes gh-21145

Closes gh-21144

Closes gh-21143

Closes gh-21142

Closes gh-21141

Closes gh-21140

Closes gh-21139

Closes gh-21138

Improve "@ConfigurationProperties vs. @Value" documentation with the
recommendation that kebab-case is used with the `@Value` annotation.

Closes gh-20507

Closes gh-21095

Closes gh-21084

Add how-to documentation describing how health information can be
exported to a Micrometer Gauge.

Closes gh-18329

Closes gh-19782

Update `JarURLConnection` to ensure that when connections are opened
a new copy of the JarFile is provided.

Prior to this commit, a single `JarFile` instance was shared which meant
that it could be accidental closed if accessed via
`JarURLConnection.getJarFile()`. If the underlying jar file is closed
then it's possible for a `NoClassDefFoundError` to be thrown if running
on JDK 11 with an active `SecurityManager`.

Closes gh-17796

Update `WebMvcAutoConfiguration` to automatically apply cors
configuration to the `WelcomePageHandlerMapping`.

Fixes gh-21048

Update `NettyWebServer` so that the `PortInUseException` is not thrown
for permission denied errors.

Fixes gh-19807

Update classes that throw `PortInUseException` so that they also
include the cause. Prior to this commit the cause was not included
which could make diagnosing the real cause difficult.

See gh-19807

Update the reference documentation with more details about how relaxed
binding works against environment variables.

Closes gh-18215

Closes gh-19972

Update `ExposeExcludePropertyEndpointFilter` so that patterns will
also match endpoint IDs that contain a dash.

Closes gh-20997

Refine `DataSourceAutoConfiguration` conditions so that an empty
`spring.datasource.url` property can be used to enable the embedded
source.

Fixed gh-20996

Closes gh-20978

Closes gh-20976

Closes gh-20623

See gh-20941

See gh-20940

See gh-20939

See gh-20938

See gh-20937

Closes gh-20678

Since the branch name doesn't always correspond to the milestone name,
eg, master.

See gh-20680

This is done by checking for existing issues only in the milestone
corresponding to the current branch. For issues, the milestone is assigned
at the time of issue creation. For PRs, since the branch is different the
milestone can be derived from that while triaging the issue.

Closes gh-20680

* pr/20756:
  Upgrade to Docker 19.03.8 in CI

Closes gh-20756

See gh-20756