fix: course mode added to the metadata

[Inferato]

Description

This is a backport MR to the master branch.

According to the chapter Sending Email Messages to Learners in Different Enrollment Tracks course can may more than one mode and instructor must have the ability to send the email for users in this modes.
Communication MFE had a hardcoded 2 modes for every course. Sometimes it lead to the error.

courseModes was added to courseMetadata to display real course email recipient options.

Related MR:

• frontend-app-communications/open-release/quince.master
• frontend-app-communications/master

Deadline

None

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[mariajgrimaldi]

Hi there @Inferato! We usually backport PR(s) after their corresponding master PR is merged. So we'll review this contribution against quince.master once that happens. Thanks!

[dyudyunov]

Just for history:
Related PR for the Communications MFE was reopened: openedx/frontend-app-communications#192

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