Add Actuator and Reference documentation for the `/logger` endpoint.
This documentation includes information on listing, reading, and
modifying the configuration of loggers.

Closes gh-7390
See gh-7086

Ensure all LoggingSystem implementation provide a consistent ROOT logger
name. Prior to this commit the `/loggers` endpoint could return '' for
root loggers which could then not be set using a POST.

Fixes gh-7372

Remove the empty logger as it was not also defined in `defaults.xml`
and caused rendering issues with the new `/loggers` endpoint.

Fixes gh-7386

Rename `ApplicationStartedEvent` to `ApplicationStartingEvent` to
avoid confusion.

Fixes gh-7381

Update `LoggersEndpoint` to additionally return the log levels actually
supported by the system.

Fixes gh-7396

See gh-7385

Closes gh-7384

* pr/7370:
  Upgrade Thymeleaf 3 layout dialect in doc

Closes gh-7370

See gh-7108

* gh-7323:
  Upgrade to Log4j 2.7

Closes gh-7323

Closes gh-7355

Closes gh-7359

Closes gh-7366

The CloudFoundryHealthMvcEndpoint does not perform additional
security checks since security is handled by the interceptor.

See gh-7108

See gh-7108

Closes gh-7347

Artemis's on-demand queue cretaion appears to be rather flakey,
sometimes failing with a NullPointerException.

This commit ensures that the queue used by the sample is created
during start up rather than on demand. This will hopefully make the
test that runs the sample more robust.

Closes gh-7346

The changes made in 6a2ac080 mean that getSecurity() on
ManagementServerProperties will no longer return null when Spring
Security is on the classpath. This had the unwanted side-effect of
causing the health endpoint to hide its details when Spring Security
was not on the classpath.

This commit reinstates the previous behaviour by only considering
the health endpoint to be secure if Spring Security is on the
classpath and management.security.enabled is true.

Closes gh-7345

Closes gh-7334

* gh-7334:
  Reinstate LaunchedURLClassLoader's registration  as parallel capable