[JENKINS-30613] Code clean-up

Make changelog URL a build parameter

Add new plugin labels to clean up Plugin Manager

[JENKINS-10547, JENKINS-22685] Update windows-slave-installer dependency to 1.5

Jenkins issues: JENKINS-10547, JENKINS-22685

Changes in winsw:
* https://github.com/kohsuke/winsw/issues?q=milestone%3Awinsw-1.17
* kohsuke/winsw@2bf9e85

Changes in the module:
* https://github.com/jenkinsci/windows-slave-installer-module/commit/a4d2121812fe9fe1b38bbe9d2cb57b9cd5435a0d
* https://github.com/jenkinsci/windows-slave-installer-module/commit/3fbc8434aba05d5d36f52f345d9d0176e98459be

Improve readability of Jenkins.getTarget()

[JENKINS-30395] Occasional ClosedByInterruptException

The ~dozen inlined options and braceless conditional weren't the easiest
to read, especially with the one compound statement in there. Took me a
minute to convince myself that operator precedence & associativity
really made that work as intended.

I *think* those strings could drop their slashes and be combined with
the other loop (e.g. go over
Sets.concat(ALWAYS_READABLE_PATHS, getUnprotectedRootActions()), but
without spending more time confirming that, I'm leaving the behavior
exactly the same as it was before.

[JENKINS-30139] Switch from a big fat lock to a concurrent collection

[JENKINS-30374] Update obsolete help message

Remove obsolete reference to "location you configured above" since the location is now determined automatically rather than explicitly configured.