Documentation now matches UI copy

What does this MR do?

Documentation fell out of step with UI copy changes.

This fixes that, and makes some other minor improvements.

Related issues

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56783.

Author's checklist

• Apply the correct labels and milestone
• Port the MR to EE (or backport from CE): https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9325

Review checklist

• PM's review (recommended, but not a blocker)
• Merge the EE-MR first (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9325), CE-MR afterwards