Ignore case for filter methods

[ARandomPerson07]

Description

Added the ability to ignore case sensitivity when filtering PDF elements by text matching. Default is not to ignore (i.e. doesn't break logic with previous versions).

Linked issues

closes #371

Testing

Created a simple PDF with various uppercase-lowercase combinations. Compared length of filtered output when the associated filter_by_text_equal and filter_by_text_contains functions are run with ignore_case as both True and False. Behaves as expected.

Testing text:

Results:

Checklist

• I have provided a good description of the change above
• I have added any necessary tests
• I have added all necessary type hints
• I have checked my linting (docker-compose run --rm lint)
• I have added/updated all necessary documentation
• I have updated CHANGELOG.md, following the format from
  Keep a Changelog.

[jstockwin]

Hey @ARandomPerson07, appreciate it's now over a year later (apologies for that, finding time is hard...).

If you wanted to resolve conflicts on the PR I'd get it in. Obviously no worries if you're no longer interested/no longer have time.