doc: Remove capitalization in man page headings
The man page builder of Sphinx already takes care of that to align with man pages conventions, and the non-capitalized output looks better in html doc.
GitLab Maintenance scheduled for Thursday, 18th December 2025, from 7:00 AM to 10:00 AM BST. GitLab will be in read-only mode and experience short periods of complete downtime (up to 20 minutes) during this window.
The man page builder of Sphinx already takes care of that to align with man pages conventions, and the non-capitalized output looks better in html doc.