Add regular expression support to list of user agents to exclude #16766

Description:

• Added regex support to Administration -> Websites -> Settings ->
  Global list of user agents to exclude
• Made sure old tests that use stripos() pass
• Added new tests
• Added a sentence to the inline help area about regex support
• Fixed a typo elsewhere as specified in the original issue.

Closes #14186.

Review

• [ ] Functional review done
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done see checklist
• [ ] 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

@nina-py could you maybe merge in the latest changed from 4.x-dev? If tests are passing, guess this PR would be good to merge as well.

@sgiehl, there are some System tests that I need to update first, and go over the UI tests to see if any failures are relevant to changes in this PR. I'll get to it over the next couple of days!

Hi @sgiehl, I've rebased the branch once again, updated the failing System and UI tests and finally most checks are green! The remaining three mismatched UI screenshots are not related to the changes in this branch. Please review.

Thank you @sgiehl!

Thanks for another contribution @nina-py !