Add packaging support for unix domain sockets

[minfrin]

• Add /run/jenkins path in systemd-tmpfiles as a home for the socket
• Support JENKINS_UNIX_DOMAIN_PATH variable to pass the socket path

Added to winstone: https://github.com/jenkinsci/winstone/pull/346 / https://github.com/jenkinsci/winstone/issues/345

Testing done

• jenkins.war from most recent master

• RPM created as follows:

WAR=/home/minfrin/jenkins.war MSI= BUILDENV=env/release.mk BRAND=branding/jenkins.mk make rpm

• /etc/sysconfig/jenkins modified for testing as follows:

JAVA_HOME=/etc/alternatives/jre_17

JENKINS_PORT=-1
JENKINS_PREFIX=/jenkins
JENKINS_UNIX_DOMAIN_PATH=/var/run/jenkins/jenkins.socket

Apache httpd configured as follows:

  ProxyPass unix:///run/jenkins/jenkins.socket|http://localhost/jenkins nocanon
  ProxyPassReverse unix:///run/jenkins/jenkins.socket|http://localhost/jenkins

### Submitter checklist
- [x] Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!
- [x] Ensure that the pull request title represents the desired changelog entry
- [x] Please describe what you did
- [x] Link to relevant issues in GitHub or Jira
- [x] Link to relevant pull requests, esp. upstream and downstream changes
- [ ] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[timja]

cc @kmartens27 / @MarkEWaite for changelog