Allow setting exit node in Tailscale

[johnpc]

I am using an exit node that I'd like to run all my Umbrel's traffic through.

It is easy to set the exit node on other devices (see screenshots of how this is set on Mac and iOS devices)

iOS UI to set exit node:

Mac OS UI to set exit node:

However, Umbrel's Tailscale Web UI has nowhere for me to set which exit node to use:

Note that I don't want to use my Umbrel as an exit node. I want to point my umbrel to use my preferred exit node.

[johnpc]

See also https://community.umbrel.com/t/make-tailscale-use-exit-node/11229/5

It appears to be a limitation of the tailscale docker image.

The docker image documents a TS_EXTRA_ARGS environment variable which passes extra args to tailscale set (see https://tailscale.com/kb/1282/docker/)

tailscale set allows the --exit-node <ip|name> flag (see https://tailscale.com/kb/1080/cli/#set)

Therefore we should be able to update the docker-compose.yml to use that environment variable like so:

services:
  web:
    network_mode: "host" # TODO: We can remove this later with some iptables magic
    image: tailscale/tailscale:v1.48.1@sha256:51c756718c30b15d1d3d228b1f4425cba646ec15da5d188a0d55c32b8ea4f378
    restart: on-failure
    stop_grace_period: 1m
    command: "sh -c 'tailscale web --listen 0.0.0.0:8240 & exec tailscaled --tun=userspace-networking'"
    volumes:
      - ${APP_DATA_DIR}/data:/var/lib
    environment:
      TS_EXTRA_ARGS: "--exit-node <ip|name>"