please conform to the newer ~/.config/rcon-cli dotfile standard

I'd be happy to submit a PR making this change as long as you'll give me some acceptance criteria :)

It could be made backwards compatible by falling back to ~/.rcon-cli.yaml for example

Start by locating how rcon-cli currently reads ~/.rcon-cli.yaml and where configuration-path behavior is defined. Before implementation, get acceptance criteria for the newer ~/.config/rcon-cli convention and backward compatibility; done should include agreed behavior for both paths and verification that existing configuration still works.

Written by the indexing model from the issue text.