Adds a page for push notifications under /guides. The main thing it covers are how push works in Matrix, UnifiedPush usage and selfhosting, and some troubleshooting of common push issues.
I took the liberty to include various aspects of push not pertaining to the server itself, because it was commonly asked in our chatrooms and are quite important for all matrix users. Kind of like livekit.
Closes#2136
Reviewed-on: https://forgejo.ellis.link/continuwuation/continuwuity/pulls/2244
Reviewed-by: Jade Ellis <jade@ellis.link>
Reviewed-by: Henry-Hiles <henry@henryhiles.com>
Reviewed-by: lveneris <tyler@kludgecs.com>
stratself