Document cookie, PASSWORD and HASHED_PASSWORD environment variables

Steps to Reproduce

1. echo -n "thisismypassword" | npx argon2-cli -e
2. HASHED_PASSWORD="<hash>" code-server
3. Try logging in

Expected

It should work

Actual

Incorrect password

Reported here https://github.com/coder/code-server/discussions/4684

[ykazakov]

Same problem here with the only difference that we use the key cookie to (automatically) authenticate the users as mentioned here.

B.t.w., I searched the docs and neither the environment variables PASSWORD or HASHED_PASSWORD, nor the authentication cookie key are mentioned anywhere. The environmental variables are mentioned in code-server --help but not the cookie. Should these things be documented or are they subject to changes?

[gerardo-junior]

+1 on https://docs.linuxserver.io/images/docker-code-server