fix: hardcoded course mode checkboxes

[dyudyunov]

This is a backport of #191

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.

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Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

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##             open-release/quince.master     #192   +/-   ##
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  Coverage                              ?   83.23%           
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  Lines                                 ?      692           
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  Hits                                  ?      576           
  Misses                                ?      116           
  Partials                              ?        0           

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