#1277 Improve documentation for development and release processes

• Improved development process documentation:
  • We don't use the GitFlow branching model anymore.
  • Update reason for no draft merge requests from the start.
  • Committers must not only regularly commit, but also regularly push.
• Improved release process documentation:
  • It is better to create the news item merge request upfront.
  • Small textual improvements.
  • Wait a bit longer for website deployment, as it can take longer.
  • Prefer auto-closing release issue when merging new item merge request.
  • Inline removal/archiving version identification into each step.

No end-user visible changes.

Addresses #1277 (closed)