This commit adds the support for static and templated welcome pages with
Spring WebFlux. The implementation is backed by a `RouterFunction`
that's serving a static `index.html` file or rendering an `index` view.

Closes gh-9785

Prior to this commit, a default tag of 'latest' was used when no tag
was included in the builder image name used when building an image in
the Maven and Gradle plugins, but the tag for the run image was left
empty if it was not provided. This resulted in errors when pulling
the run image from an image repository. This commit applies the
same tag defaulting logic to the run image name.

Fixes gh-21532

Closes gh-21529

* pr/21485:
  Fix typo in section 4.30.6

Closes gh-21485

See gh-21485

* pr/21509:
  Avoid allocations in ConfigFileApplicationListener

Closes gh-21509

See gh-21509

Closes gh-21524

Closes gh-21526

Closes gh-21525

Closes gh-21528

Closes gh-21527

Closes gh-21282

* gh-21490:
  Polish `Add gradle build image command line example`
  Add gradle build image command line example

Closes gh-21490

See gh-21490

See gh-21490

Closes gh-21522

Fixes gh-21354

Fixes gh-21518

Fixes gh-21470

* gh-21481:
  Polish

Closes gh-21481

See gh-21481

Closes gh-21473

This commit updates the MavenPublishingConventions to use HTTPS to
link to the Apache license. The configuration of NoHTTP has also
been reworked so that it will correctly find usch uses of http://
URLs.

Closes gh-21459

Closes gh-21472

Closes gh-21471

Closes gh-21466

Closes gh-21460

Update the lquibase test to use `http://` rather than `https://` so that
it can be resolved from the local jar.

Prior to this commit, the published Maven POMs would not pass the Maven
Central mandatory checks.

This commit adds the missing project name and description metadata for
most artifacts. The Spring Boot Gradle plugin artifact was also missing
this information and this is now added in the plugin metadata itself.
This is also updating the project page URL which is now hosted directly
on spring.io.

Fixes gh-21457

Fixes gh-21451

Closes gh-21450

See gh-21350

There's a bug in Undertow that means it may leak a file handle is
the server is stopped immediately after a response to an SSL request
has been received. The stop processing races with Undertow's SSL
support tidying things up after sending the response. When the stop
processing wins, the tidying up fails with a NullPointerException that
prevents an input stream from being closed. On Windows, the input
stream remaining open prevents JUnit from being able to clean up its
temporary directory.

This commit uses Awaitility to wait for the file that's being served
over SSL to be deleted before stopping the server. On Windows, this
will delay the stop processing from beginning until after the tidy up
that's performed after sending the response has been completed,
hopefully eliminating the race condition that resulted in the input
stream being left open.

Fixes gh-21172

Closes gh-17274