Improve handling of incompatible plugins during an update

[sgiehl]

Description:

Incompatible plugins can currently break the updating process, as the process might try to disable them within the process that is still running with old code. If disabling the plugin triggers code, that was not yet loaded, new files might get loaded, that contain code that can't work with the previously loaded old code.

This PR adds a new set of UI tests that will perform an update from the last (forced) Matomo version. Currently this is 4.15.0.
Note: Running this new tests with updating from 4.14.x resulted in errors, which are now fixed with using 4.15.x

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

[bx80]

This worked for me when updating a 4.15 install with an incompatible plugin, the plugin was disabled and the update completed successfully. Automated tests are all looking good and I can't see any other issues 👍