fix: hardcoded course mode checkboxes

[dyudyunov]

The Communication MFE has course mode checkboxes hardcoded, so a user can select any of them even if the course has no such mode.
As a result - they will get an error when trying to send emails to learners of the track (course mode) that doesn't exist.

The goal here is to provide course mode checkboxes for real course modes only.

[openedx-webhooks]

Thanks for the pull request, @dyudyunov! 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
• Open edX discussion forum threads
• timeline information ("this must be merged by XX date", and why that is)
• partner information ("this is a course on edx.org")
• any other information that can help Product understand the context for the PR

All technical communication about the code itself will be done via the GitHub pull request interface. As a reminder, our process documentation is here.

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (56e1781) 83.01% compared to head (41a1e81) 83.23%.
Report is 15 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #191      +/-   ##
==========================================
+ Coverage   83.01%   83.23%   +0.22%     
==========================================
  Files          46       47       +1     
  Lines         683      692       +9     
  Branches      132      135       +3     
==========================================
+ Hits          567      576       +9     
  Misses        116      116              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[arbrandes]

Looks good to me! Thanks @dyudyunov!

[openedx-webhooks]

@dyudyunov 🎉 Your pull request was merged! Please take a moment to answer a two question survey so we can improve your experience in the future.