feat(tmux): complete src/target session arguments

[jessedhillon]

This adds completion for session names. Commands which take a running session's name as an argument, for example attach-session, can now have those options completable. For example:

$ tmux list-sessions -F '#{session_name}'
bash-cmp
nix-config
$ tmux attach-session -t <tab>
bash-cmp    nix-config

I checked the tmux repo, and they do not maintain bash completions, so I'm submitting this here.

[yedayak]

Did you see src-session in output from tmux? I only found it in the tmux source, but it doesn't seem to be used currently. If we do want to have it here anyway, we should probably also have dst-session

[jessedhillon]

no, I asked an AI to look at tmux output and propose those options. I see that target-session is the only option that is used in the usage output, so we can trim this down to one option name.