.msg file upload

[robinmolen]

Closes #4795

Changes

The sdk cannot determine what content type should be used for .msg files, which results in the content type "". When you try to submit the form, the fileSerializer doesn't recognizes the content type and returns an error.

To allow the submission of .msg files, the content type should be allowed to be empty.

• Turned type property on FileSerializer optional
• Added validation for .msg files to the MimeTypeValidator

Checklist

Check off the items that are completed or not relevant.

• Impact on features

  • Checked copying a form
  • Checked import/export of a form
  • Config checks in the configuration overview admin page
  • Problem detection in the admin email digest is handled

• Release management

  • I have labelled the PR as "needs-backport" accordingly

• I have updated the translations assets (you do NOT need to provide translations)

  • Ran ./bin/makemessages_js.sh
  • Ran ./bin/compilemessages_js.sh

• Dockerfile/scripts

  • Updated the Dockerfile with the necessary scripts from the ./bin folder

• Commit hygiene

  • Commit messages refer to the relevant Github issue
  • Commit messages explain the "why" of change, not the how

[robinmolen]

The removal of the FileSerializer type blank message conflicts with #4496. Some more work is required to ensure users receive useful error messages, when needed

[robinmolen]

The MimeTypeValidator now checks if the file has an extension. If it doesn't, an validation error is raised

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.62%. Comparing base (260a985) to head (5e77364).
Report is 12 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4961   +/-   ##
=======================================
  Coverage   96.62%   96.62%           
=======================================
  Files         760      760           
  Lines       25837    25843    +6     
  Branches     3385     3388    +3     
=======================================
+ Hits        24964    24970    +6     
  Misses        608      608           
  Partials      265      265           

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