Closes gh-16347

Closes gh-16346

Closes gh-16345

Closes gh-16360

Closes gh-16359

Closes gh-16358

Fixes gh-16177

Closes gh-16404

See gh-16400

Closes gh-16400

Closes gh-16340

Closes gh-16339

Closes gh-16338

In addition to upgrading to Jetty 9.4.15, this commit updates the
KeyStores used in embedded container testing to add to their entries
subject alternative name extensions for localhost and 127.0.0.1. As
of 9.4.16, Jetty requires the SAN extensions.

Closes gh-16188

* pr/16262:
  Polish "Automatically detect log4j2.properties"
  Automatically detect log4j2.properties

Closes gh-16262

See gh-16262

Closes gh-16372

Closes gh-16387

* pr/16332:
  Disable nulls serialization when serialize-nulls property is false