docs: Add guide for remote workers

[Horstage]

Comments and changes are very welcome.

[github-actions]

Label error. Requires exactly 1 of: changelog:.*. Found:

[bo0tzz]

Thanks for the PR! There's already an overlapping guide at https://immich.app/docs/guides/scaling-immich. I've deliberately held off on details like you put here, because I worry that people will follow it blindly and expose internal ports on the internet, which will certainly get their systems hacked.