Add unit format reference to nav

I added a previously unlinked page https://docs.gitlab.com/ee/operations/metrics/dashboards/yaml_number_format.html and rearranged some nav items to be alphabetically sorted (without changing hierarchy).

Nav before	Nav after

Add navigation item to global navigation

• Link to the merge request that introduced the new page: #1220 (comment 1045066161)
• Give the MR a descriptive title.
• Link to the review app showing the new page: http://msj-link-unit-formats-ref.35.193.151.162.nip.io/ee/operations/metrics/dashboards/yaml_number_format.html