Docker: change /config/config.toml permissions so Athens can be ran as non-root user

[tzvetkoff]

Problem

Currently the /config/config.toml has permissions set to 0700.
This makes it impossible to run Athens with a non-root user, and this is in turn needed so you can mount the filesystem storage directory with your UID/GID.

Possible solution
Changing the permissions to something sane, like 0644 (or 0755 and add a #!/bin/athens-proxy hashbang.)

Alternative
Building a wrapper image is indeed an option, yet it's not as simple as docker run gomods/athens:latest -u $UID:$GID -v $PWD/data:/data -e...

Additional context
I couldn't find the Dockerfile used to build https://hub.docker.com/r/gomods/athens, otherwise I would've sent a PR (even though it's a 1-line change.)

[endocrimes]

@tzvetkoff looks like this is the dockerfile they use for pushing those images https://github.com/gomods/athens/blob/main/cmd/proxy/Dockerfile

[arschles]

Thanks for the pointer @endocrimes 😊

@tzvetkoff feel free to send a pull request - we'd really appreciate that!