Add "last updated" date to the bottom of pages in the docs

[kmalloy24]

The speed the team is putting out new features and improvements is really impressive! However, sometimes the docs have a hard time keeping up. A date tag at the bottom of each page would be very helpful when comparing depreciated information. For example, the Build a User Management App with SvelteKit Tutorial uses auth-helpers-sveltekit and makes no mention of the new @supabase/ssr package.