Upgrade maven-pmd-plugin to 3.22.0 which uses PMD 7 by default

[mprins]

This upgrades to the current release of the maven-pmd-plugin which uses PMD 7.0.0 by default.
While at it also update the build steps in the GH workflow
In 7.0.0 some rules have changed, this requires some changes in the selected rules.
As a result some PMD warnings are now triggered that need fixing.

Checklist

• I have read the contribution guidelines.
• I have sent a Contribution Licence Agreement (not required for small changes, e.g., fixing typos in documentation).
• First PR targets the main branch (backports managed later; ignore for branch specific issues).
• All the build checks are green (see automated QA checks).

For core and extension modules:

• New unit tests have been added covering the changes.
• Documentation has been updated (if change is visible to end users).
• The REST API docs have been updated (when changing configuration objects or the REST controllers).
• There is an issue in the GeoServer Jira (except for changes that do not affect administrators or end users in any way).
• Commit message(s) must be in the form [GEOS-XYZWV] Title of the Jira ticket.
• Bug fixes and small new features are presented as a single commit.
• Each commit has a single objective (if there are multiple commits, each has a separate JIRA ticket describing its goal).

[aaime]

Nice one! Ambitious, too 🤣
I'll see if I can help, but can't promise anything in the short term.

[mprins]

This turns out to be much more work than anticipated, unfortunately I've no run out of time due to upcoming holiday, so this PR will stall from my side for a couple of weeks. Anyone willing to spend some time on it is quite welcome 🤣

[aaime]

Migrated a couple of modules while I was travelling.

[aaime]

And a few more under "web" (but not all yet)