Move plugin related sub menu items to new Plugins menu item

[sgiehl]

Description:

fixes DEV-17433

Note: Some UI tests are failing because of the menu changes. I've created separate PRs to fix them:

CustomAlerts: matomo-org/plugin-CustomAlerts#153
CustomVariables: matomo-org/plugin-CustomVariables#80
PrivacyManager: #21607
Login (Brutefoce Log): #21608
API error: #21615

Review

• Functional review done
• Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• Documentation added if needed
• Existing documentation updated if needed

[caddoo]

Tested locally and functionally is good.
Code is fine as well.

There are some unrelated UI expected screenshots that have been updated, is that just an unrelated clean up so they pass?

[sgiehl]

Yes. Those are flaky tests that failed a lot with the previous versions. But they still fail sometimes with the updated files 🤷