Clarify release flow

The current release flow is

1. Run pre-release action, entering the version tag to release (1.2.3)
2. Approve the resulting PR
3. Merge that PR after tests have run
4. Run release action, re-entering the version tag to release (1.2.3) and skipping the first `If enabled, the version bump, release notes update and tag creation will be skipped. Select this option if those tasks have already been done in a previous run` section
5. Approve and merge the post release PR that merges to the 1.x branch, needed for the docs update (while the create github release action is waiting)

Suggested clarifications:
- rename `pre release` action to `release-part1`
- rename `release` action to `release-part2`
- rename `pre post release` action to `release utility steps`
- remove the `skip_preparation` steps and check from `release.yml`