Support env var substitution in proxy.auth_secret

[hmk]

I could not get env var substitution in the proxy.auth_secret to work. It appears may not be supported yet.

Describe what you are trying to accomplish and why in non technical terms
I want to be able to set the auth_secret for my proxy in an environment variable, so I can keep this secret out of git.

Describe the solution you'd like
Env var substition, similar to how it happens in other parts of the

Additional context
If I am wrong, and it is supported... apologies (I will dig into why I couldn't get it to work).

If I get confirmation from others that this is not supported and is of interest, I'm happy to draft a PR to make it happen.

[hawkeye217]

This is already supported. You need this format:

proxy:
  auth_secret: "{FRIGATE_PROXY_SECRET}"

The code uses EnvString, which is exactly what is used elsewhere for other environment variable substitutions.

frigate/frigate/config/proxy.py

Line 40 in 573a5ed

auth_secret: Optional[EnvString] = Field(

If you try the format above and are still having issues, feel free to open a support discussion.