Update gitlab templates

What does this MR do?

Update existing GitLab Description Templates. Changes:

• MR-from-task:

  • Suggest "Squash commits" option

    Rationale: After merging, commits from the previous branch are rarely ever reverted. Squashing before merging helps keeping the master log cleaner. Additionally, the number of commits is no real indication of time/effort spend on code.

    Downside: The default squash commit message is the message of the first commit that deviates from the target branch. This message usually has to be updated/changed right before merging (changes are not stored). The squash commit author is the author/creator of the merge request, whereas the author of the merge commit is the person performing the merge.

  • Suggest "Delete branch after merge" option

• bug-report:
  • Reduce headline level
  • Add table for reporting input files, suggested in https://ts-gitlab.iup.uni-heidelberg.de/dorie/dorie/issues/79#note_13019

Add new Templates:

• version-rollout: Release of a new minor or major version.
• patch-release: Release of a bugfix/patch update (Issue and MR templates).

Is there something that needs to be double checked?

• Templates looking good when parsed by GitLab

Can this MR be accepted?

• Added/Updated templates
• Pipeline passing
• Added entry to CHANGELOG.md
• Squash commits option set
• Delete branch option set

Related issues

Closes #79 (closed)