docs: release can't be pushed to main

Description

Fixes #1400 (closed)

This MR changes the release process to create Release MRs instead of push the version bump directly to main.

We had several issues recently when maintainers pushed to main by accident.

This process improvement is taken from https://gitlab.com/gitlab-org/editor-extensions/gitlab-lsp#releases, the script to prevent squashing the MR comes from the LS as well.

After this MR is merged, we can prevent maintainers from pushing to main.

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes