Adds catalog-info.yaml and updates README as per OEP-55

[pomegranited]

Following the steps in How to maintain a repo, this PR:

• adds catalog-info.yaml to record maintainership in Backstage
• updates README.rst to use current cookiecutter format.
• moves LICENSE to LICENSE.txt to match cookiecutter defaults.

Testing instructions:

To test this change, please follow the updated README#getting-started-with-development

Author Notes & Concerns

This repo has docs, but they're not published to docs.openedx.org yet.

Could someone with access please add them? Procedure noted here: https://openedx.atlassian.net/wiki/spaces/DOC/pages/21627535/Publish+Documentation+on+Read+the+Docs

[openedx-webhooks]

Thanks for the pull request, @pomegranited! Please note that it may take us up to several weeks or months to complete a review and merge your PR.

Feel free to add as much of the following information to the ticket as you can:

• supporting documentation
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Please let us know once your PR is ready for our review and all tests are green.

[pomegranited]

Hi @feanil @sarina sorry to bug you directly, but I don't think there's anyone else on the CC/maintainer list for this repo.

Could one of you review this PR when you get a chance?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.43%. Comparing base (0106916) to head (609553a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #233   +/-   ##
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  Coverage   93.43%   93.43%           
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  Files          18       18           
  Lines        1995     1995           
  Branches      130      130           
=======================================
  Hits         1864     1864           
  Misses        118      118           
  Partials       13       13           

Flag	Coverage Δ
unittests	93.43% <ø> (ø)

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[sarina]

Looks good!