Upgrade script notes and fix for 1.16 on Debian

[Donnype]

Changes

This does an extra check on organization existence and adds some documentation to the release notes for the Debian packages.

Issue link

Closes #3728

Demo

QA notes

This is hard to really QA and I checked with a user already, so consider this one QA'd perhaps? Please double check the docs!

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Code Checklist

• All the commits in this PR are properly PGP-signed and verified.
• This PR only contains functionality relevant to the issue.
• I have written unit tests for the changes or fixes I made.
• I have checked the documentation and made changes where necessary.
• I have performed a self-review of my code and refactored it to the best of my abilities.

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Checklist for code reviewers:

Copy-paste the checklist from the docs/source/templates folder into your comment.

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Checklist for QA:

Copy-paste the checklist from the docs/source/templates folder into your comment.

[sonarcloud]

Quality Gate failed

Failed conditions
25.2% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud