Cosign improvements (batch 2)

[sergei-maertens]

Closes #4320 (partially)

Changes

• Added new templates with (roughly) the desired language/literals for the confirmation email sent to the submitter
  • handles the state when cosign is not done yet (so right after submitting)
  • handles the state when the cosigner has done the signing and a confirmation is sent that it's now processed
• Update documentation
• The summary PDF no longer includes the confirmation page content template for cosign, instead it includes a disclaimer that the submission is not guaranteed to be processed yet.

Screenshots

E-mail to submitter before cosigning

E-mail to submitter after cosigning

PDF generated

Checklist

Check off the items that are completed or not relevant.

• Impact on features

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

• Release management

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

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

  • [x] Ran ./bin/makemessages_js.sh
  • [x] Ran ./bin/compilemessages_js.sh

• Commit hygiene

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

[codecov[bot]]

Codecov Report

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

Project coverage is 96.58%. Comparing base (e4fb7bb) to head (774fad2).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #4838 +/- ## ========================================== - Coverage 96.58% 96.58% -0.01% ========================================== Files 749 750 +1 Lines 25531 25589 +58 Branches 3376 3387 +11 ========================================== + Hits 24659 24715 +56 - Misses 608 610 +2 Partials 264 264 ```

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[sergei-maertens]

Putting this one up for review - however keep in mind that I want to do a refactor follow-up PR:

• I want some kind of utility/container that captures the cosign information for a submission. Now a bunch of information/properties/methods are scattered on the Submission model and while I like fat models, this one is getting obese
• There are a couple more textual changes to apply and tweak, so that will be a separate PR too.