Read REDIS password from /var/run/redis/auth/passwd

[XioNoX]

Trying your exporter on Dell SONiC 4.0.5 and I noticed that the password is hardcoded as empty string in https://github.com/kamelnetworks/sonic_exporter/blob/main/sonic_exporter.go#L131

I don't know when this changed, but my SONiC version requires a password

$ docker run -v /var/run/redis:/var/run/redis:ro ghcr.io/kamelnetworks/sonic_exporter
level=info msg="Starting up" exporter-git-hash=e1d7f32 exporter-version=0.2.0 lib-node-version=v1.3.1 lib-prometheus-version=v1.11.0
level=fatal msg="Failed to read configuration from redis: NOAUTH Authentication required.  "

However that is conveniently sitting in:

$ cat /var/run/redis/auth/passwd 
aaabbbcccddddeeefff==

(password modified here, but to show that it's the only string in the file).

Possible behavior is to check if the file exists and in that case try to use it. Then try an empty string if no success.

Once this is solved and I get it working, I'll be happy to give the steps needed for it, as for example neither sonic-package-manager nor "SONiC click" exist on this version.