A layout can
also optionally change the loader jar that is unpacked in the root
of the repackaged archive by implementing a new method in Layout.

Instead of a fixed enum of layout types, user can provide custom
layouts via implementations of LayoutFactory in spring.factories.

* pr/7215:
  Polish contribution
  Update documentation on Actuator hypermedia support

Closes gh-7215

Spring Boot Actuator hypermedia support has been disabled by default via
c7c685f6, but its documentation wasn't updated.

This commit updates the documentation related to the change.

See gh-7215

Previously, the algorithm that computes the String representation of a
class reference and a property type was shared. This lead to generic
information for group's `type` and `sourceType` property.

This commit separates that logic in two: `getQualifiedName` is now
responsible to generate a fully qualified class name while the existing
`getType` is solely responsible to generate a type representation for the
property. Only the latter has generic information.

Closes gh-7236

It's more useful as a building block for other tools that way,
and it's easy to add the spring boot dependencies using public
methods.

This commit restores the logic in Handler that was changed when
d20ac56a was merged, while leaving the structural improvements intact.

In addition to a couple of changes where a typo meant the wrong
variable was being referenced, some logic branches now return false
rather than called super. This realigns our Handler's behaviour with
that of the JDK's.

Some more tests have also been added to try to catch the problems that
were introduced during the merge.

Closes gh-7021

* pr/7225:
  Polish contribution
  Allow to configure Tomcat's rotatable property

Also add rotate attribute to Undertow

Closes gh-7225

See gh-7225

* pr/7224:
  Fix indentation for spring.jms.template.* keys

Closes gh-7224

Previously our handler didn't override parseURL or sameFile which
resulted in behaviour that differed from that of the JDK's handler.
Crucially, this would result in our JarURLConnection being passed
a spec that didn't contain a "!/". A knock-on effect of this was
that the connection would point to the root of the jar rather than
the intended entry.

Closes gh-7021

Closes gh-7178

See gh-7108

* pr/7086:
  Polish `/loggers` actuator endpoint
  Add `/loggers` actuator endpoint

See gh-7086

Add `LoggersEndpoint` that can enables listing and configuration of log
levels. This actuator builds on top of the `LoggingSystem` abstraction
and implements support for Logback, Log4J2, and JUL.  The LoggingSystem
interface is modified to require each implementation to list the
configuration of all loggers as well as an individual logger by name.

The MVC endpoint exposes these behaviors at `GET /loggers` and
`GET /loggers/{name}` (much like the metrics actuator).

In addition `POST /loggers/{name}` allows users to modify the level for a given
logger. This modification is passed to the logging implementation, which
then decides, as an internal implementation detail, what the final outcome
of the modification is (e.g. changing all unconfigured children). Users
are then expected to request the listing of all loggers to see what has
changed internally to the logging system.

Closes gh-7086

Closes gh-7214

Closes gh-7174
See gh-7213

Closes gh-7202

* pr/6954:
  Improve systemd service documentation

Closes gh-6954

Closes gh-7016