update the location of the configuration file ()

[milosgajdos]

• the path should likely no longer contain "docker"; decide on a new location
• can we have some / do we need some fallback for the old location? (symlink, or ideally; binary checking both?)
• update the official image accordingly; https://github.com/distribution/distribution-library-image/blob/73483231b14174569cbc2ecaf8af15a990f460c6/Dockerfile#L32
• is there a default location that the registry uses? if so, can we remove the ENTRYPOINT and let the registry use the default location (if present)?