Closes gh-21703

Closes gh-21701

Closes gh-21699

Previously, the retry plugin was only applied on CI as we do not want
tests to be retried in local builds. Unfortunately, this arrangement
led to test tasks from CI builds having additional doFirst and doLast
actions and an additional property. These differences meant that the
output from a test task that has run on CI could not be used by a
local build.

This commit changes our configuration of the test retry plugin so
that it is now always applied. To retain the behaviour of only
retrying tests on CI, max retries is configured to 3 on CI and 0 for
local builds.

Closes gh-21698

Closes gh-21690

Update `SpringBootServletInitializer` to use the `ServletContext` that
was provided to the initial `onStartup` call rather than the
one from the `ServletContextEvent`. This allows the `getClassLoader()`
call to complete without throwing an `UnsupportedOperationException`.

Fixes gh-21684

Closes gh-21685

This commit improves the error messages returned by the Spring Boot
build plugins when a 5xx status code is returned from the Docker
API while attempting to build an image. If the error response has
contents containing a JSON structure with a "message" key, the value
associated with that key will be included in the exception message
and in the build plugin output error.

Fixes gh-21515

Closes gh-21678

* gh-21673:
  Polish Slack notification when no build scan was published

Closes gh-21673

See gh-21673

Closes gh-21677

Closes gh-21675

Closes gh-21676

Closes gh-21674

Closes gh-21669

Fixes gh-21507

Closes gh-21668

Closes gh-21453

Closes gh-21667

Closes gh-21664

Closes gh-21665

Closes gh-21663

Closes gh-20333

Closes gh-21596

Closes gh-21661

Closes gh-21660

Update `SpringConfigurationPropertySource` so that wrapped random
property sources can be used. It's assumed that wrapped random
sources will use the name of the source as the prefix.

Closes gh-21595

Closes gh-21657

Closes gh-21576

Closes gh-21656

Closes gh-21655

Fix the `containsDescendantOf` logic for random property sources to
ensure that ancestors are correctly matched.

Closes gh-21654

Closes gh-21651

Closes gh-21640

Closes gh-21649