Optimize streaming by making the RPis stream to the server (instead of proxy passing to each RPi)

[ddabble]

[Originally created on the "Dev-Web" Trello board, by @ddabble on September 3, 2022]

Currently, when multiple users are watching the same RPi’s stream, one stream connection is opened for each user, which are all handled mainly by the RPi (the website server just proxy passes all requests to each RPi through Nginx). This can be optimized by instead making the RPis stream/publish to the website server - which would mean that only one connection is every open for each RPi - and then make the website server respond to each stream request, with no proxy passing whatsoever.

See Oppsett av Octopi stream på verkstedet (an incomplete/unpolished guide) for some details on how this can be done.