See gh-19981

Closes gh-20028

* pr/19901:
  Polish contribution
  Handle message of @ResponseStatus-annotated exception with WebFlux

Closes gh-19901

See gh-19901

See gh-19901

Closes gh-20023

Closes gh-20015

This commit upgrades to spring javaformat 0.0.20 and Checkstyle 8.29.

This commit also upgrades to the Checkstyle maven plugin 3.1.0.

See gh-20011

* pr/20004:
  Polish samples in doc

Closes gh-20004

See gh-20004

Closes gh-19912

Closes gh-19932

* pr/19976:
  Update test name in WebFluxTagsTests

Closes gh-19976

See gh-19976

Closes gh-19970

Previously, only the top-level handlers were examined to find the
ContextHandlers and log the context path. If those handlers had
been wrapped, this prevented the ContextHandlers from being found
and an empty string was always logged.

When finding the context path, this commit unwraps the handler held
by a HandlerWrapper until the ContextHandler is found.

Fixes gh-19969

Closes gh-19965

* pr/19961:
  Fix Gradle plugin documentation links

Closes gh-19961

See gh-19961

Closes gh-19962

* pr/19944:
  Replace deprecated Concourse resource for pull requests

Closes gh-19944

See gh-19944

Closes gh-19957

* pr/19956:
  Fix typo

Closes gh-19956

See gh-19956

See gh-19936

* pr/19902:
  Upgrade to Testcontainers 1.12.5

Closes gh-19902

See gh-19902

Closes gh-19928

* pr/19913:
  Upgrade CI images to Ubuntu Bionic 20200112

Closes gh-19913

See gh-19913

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-19872