Closes gh-19906

* pr/19762:
  Add Gradle Wrapper Validation GitHub Action

Closes gh-19762

See: https://github.com/gradle/wrapper-validation-action
See gh-19762

* pr/19896:
  Remove obsolete files

Closes gh-19896

See gh-19896

Closes gh-19904

Closes gh-19903

Closes gh-19645

* pr/19880:
  Polish "Close TomcatMetrics on shutdown for cleanup"
  Close TomcatMetrics on shutdown for cleanup

Closes gh-19880

See gh-19880

See micrometer-metrics/micrometer#1424
See gh-19880

Closes gh-19639

* pr/19776:
  Test the Gradle Plugin against Gradle 6.1

Closes gh-19776

See gh-19776

Closes gh-19877

See gh-18621

See gh-18621

The Cassandra v4 driver does not longer have automatic local DC inference
from contact points. As a result, the "local-datacenter" property must be
set with the default load balancing policy and the contact points must
be of that data center.

This commit adds a new property for the local datacenter so that it can
be specified without the use of a customizer.

Closes gh-19779

Closes gh-19878

Closes gh-19830

See gh-19830

Previously \r\n was used on Windows and \n was used on other
platforms. This resulted in different JSON content being written to
the archive. As the config's entry name is the SHA-256 hash of its
content, it also resulted in the entry name being different.

This commit updates the JSON that's written into the archive to use
\n line endings, irrespective of the OS on which the image is being
built.

See gh-19828

See gh-19828

* gh-19863:
  Fix TestFailuresPlugin.TestFailure.compareTo()

Closes gh-19863

This commit also polishes around it a bit.

See gh-19863

We build with Java 8, 11, and 13 without specifying target
compatibility for the bytecode of the app that's placed in the image.
The built image uses Java 11 and when the app is built with Java 13
it fails to start as the Java 11 VM can't read that Java 13 bytecode.

This commit configures the app that's placed in the image to be built
with target compatibility of 1.8. This allows it to be compiled with
all version of Java with which we build and to also be compatible
with the JVM that's in the image.

See gh-19831

Closes gh-19874

Closes gh-19824

https://repo.spring.io/snapshot should only be available when
building a BUILD-SNAPSHOT. https://repo.spring.io/milestone should
only be available when not building a RELEASE (a BUILD-SNAPSHOT, Mn,
or RCn).

Closes gh-19700

Closes gh-19867

Closes gh-19792

Closes gh-19831

See gh-19847
See gh-19792

This commit changes uses of ClassLoader.loadClass to Class.forName for
consistency with what was initiated in #19342 and better compatibility
with GraalVM.

Closes gh-19824

* pr/19764:
  Upgrade to Kafka 2.4.0 and Spring Kafka 2.4.1

Closes gh-19764

See gh-19764