Closes gh-15937

Closes gh-15938

See gh-15197

* pr/15933:
  Polish "Fix broken links to appendix"
  Fix broken links to appendix

Closes gh-15933

See gh-15933

Closes gh-15862

Closes gh-15878

See gh-15775

Closes gh-15890

Closes gh-15348

When Spring Security is misconfigured it's possible to switch from an anonymous user
to a normal user. When switching back again, the corresponding
AuthenticationSwitchUserEvent will have a null target user. Previously, Actuator's
AuthenticationAuditListener would throw a NullPointerException when it received such an
event.

This commit updates the audit listener to defensively handled events with a null target
user.

Closes gh-15767

* pr/15859:
  Polish contribution
  Polish 'Database Initialization' section

Closes gh-15859

See gh-15859

* pr/15580:
  Polish "Change "Colophon" to "Legal""
  Change "Colophon" to "Legal"

Closes gh-15580

See gh-15580

* gh-15775:
  Polish "Use class for @ConditionalOnClass"
  Use class for @ConditionalOnClass

Closes gh-15775

See gh-15775

See gh-15775

* pr/15325:
  Polish "Support for capping archived log files"
  Support for capping archived log files

Closes gh-15325

See gh-15325

* gh-7630:
  Polish "Add TestNG support in TestTypeExcludeFilter"
  Add TestNG support in TestTypeExcludeFilter

Closes gh-7630

See gh-7630

See gh-7630

This reverts commit 1f47bd97.

See gh-15915

* gh-15842:
  Polish "Make auto-config of RestTemplate metrics back off with no builder bean"
  Make auto-config of RestTemplate metrics back off with no builder bean

Closes gh-15842