Expose UDP in reverse proxy mode (http3)

[addy419]

I came across this PR #3515 which disabled UDP when apache container is in reverse proxy mode. Caddy now has support for reverse proxying http3 https://caddyserver.com/docs/caddyfile/directives/reverse_proxy#versions so I think we should make it configurable (with a env var maybe?)

[Zoey2936]

http3 only work with tls, since the reverse proxy mode uses http unencrypted, quic would not work

[addy419]

Hmm, makes sense. But is it okay to leave the Caddy connection (to the outside world) as http3? My caddy logs show this error every time I refresh the page, whereas it wasn't there when the apache container was serving nextcloud directly to 443

{"level":"error","ts":1735505837.2040484,"logger":"http.handlers.reverse_proxy","msg":"aborting with incomplete response","upstream":"localhost:11000","duration":0.00205759,"request":{"remote_ip":"85.255.234.33","remote_port":"35158","client_ip":"85.255.234.33","proto":"HTTP/2.0","method":"GET","host":"nextcloud-domain.com","uri":"/apps/files/img/app.svg","headers":{"Cookie":["REDACTED"],"Sec-Fetch-Dest":["image"],"Sec-Gpc":["1"],"X-Forwarded-Proto":["https"],"Accept-Language":["en-US,en;q=0.5"],"Sec-Fetch-Mode":["no-cors"],"User-Agent":["Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:133.0) Gecko/20100101 Firefox/133.0"],"Dnt":["1"],"X-Forwarded-For":["85.255.234.33"],"X-Forwarded-Host":["nextcloud-domain.com"],"Accept-Encoding":["gzip, deflate, br, zstd"],"Sec-Fetch-Site":["same-origin"],"Te":["trailers"],"Priority":["u=4, i"],"Accept":["image/avif,image/webp,image/png,image/svg+xml,image/*;q=0.8,*/*;q=0.5"]},"tls":{"resumed":false,"version":772,"cipher_suite":4865,"proto":"h2","server_name":"nextcloud-domain.com"}},"error":"reading: context canceled"}