docs: [FC-0074] add naming suggestions to use when creating new filters

[mariajgrimaldi]

Description

This PR adds naming suggestions for implementing new Open edX Filters.

Testing instructions

You can see the docs rendered here:

Deadline

"None" if there's no rush, or provide a specific date or event (and reason) if there is one.

Checklists

Check off if complete or not applicable:

Merge Checklist:

• All reviewers approved
• Reviewer tested the code following the testing instructions
• CI build is green
• Version bumped
• Changelog record added with short description of the change and current date
• Documentation updated (not only docstrings)
• Code dependencies reviewed
• Fixup commits are squashed away
• Unit tests added/updated
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

Post Merge:

• Create a tag
• Create a release on GitHub
• Check new version is pushed to PyPI after tag-triggered build is
  finished.
• Delete working branch (if not needed anymore)
• Upgrade the package in the Open edX platform requirements (if applicable)

[openedx-webhooks]

Thanks for the pull request, @mariajgrimaldi!

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