Email ingestion from Exchange.

[elcct]

Description of change

This changes where emails are ingested from, as we moved from S3 to Exchange.
It also switches the email processor from calendar to plain email.

Checklist

• Has this branch been rebased on top of the current main branch?

  Explanation

  The branch should not be stale or have conflicts at the time reviews are requested.

• Is the CircleCI build passing?

General points

Other things to check

• Make sure fixtures/test_data.yaml is maintained when updating models
• Consider the admin site when making changes to models
• Use select-/prefetch-related field lists in views and search apps, and update them when fields are added
• Make sure the README is updated e.g. when adding new environment variables

See docs/CONTRIBUTING.md for more guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.60%. Comparing base (02bd991) to head (41ef911).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5829      +/-   ##
==========================================
+ Coverage   96.52%   96.60%   +0.08%     
==========================================
  Files        1046     1046              
  Lines       24889    24902      +13     
  Branches     1649     1647       -2     
==========================================
+ Hits        24024    24057      +33     
+ Misses        709      689      -20     
  Partials      156      156              

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[samuele-mattiuzzo]

@elcct left a couple of comments, but can still approve otherwise

[samuele-mattiuzzo]

Also, looks like it needs more tests