Support subpaths

[SmilyOrg]

Is your feature request related to a problem? Please describe.
Currently the app requires to be deployed to a (sub)domain at the root folder (/)

Describe the solution you'd like
Support being able to access it from a subpath, e.g. /gallery

Describe alternatives you've considered
Not supporting it as it might have security implications (some cross-domain checks do not apply). Requires a little research.

Additional context
See https://lemmy.world/comment/7833393

[gardiol]

Finally come round to test it, and i can't because of this. I do not want to spin a subdomain just for testing as it would be the n-th...
Please add it :)

[gardiol]

I love the simplicity and the fact that it can be self hosted on bare metal. Keep up the amazing work!