feat: removed never from cadence options

[muhammadadeeltajamul]

Description

• Removed Never option from email cadence preference
• Set SHOW_EMAIL_CHANNEL to true in .env.development

How Has This Been Tested?

Click on email cadence dropdown in course preferences page

Screenshots:

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 58.61%. Comparing base (d0fdc2a) to head (dee2d6e). Report is 9 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1142 +/- ## ======================================= Coverage 58.61% 58.61% ======================================= Files 117 117 Lines 2317 2317 Branches 641 641 ======================================= Hits 1358 1358 Misses 898 898 Partials 61 61 ```

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