Add shell completions

[orhun]

lychee_bin already uses clap which means we can utilize the following crates:

• clap_complete: generated the shell completions
• clap_mangen: generated manpage

Then downstream sources (i.e. package managers) can consume the generated files :)

[thomas-zahner]

Yeah, that would definitely be two great improvements. This partially duplicates #1505

[mre]

Closing in favor of #1505. Will reverence the clap tools over there. Thanks!

[thomas-zahner]

I'm reopening this since I'm addressing the man page generation in #1858 but not yet shell completions. This is why I renamed the issue from Add shell completions and manpage to Add shell completions.

Note that we should use the --generate flag to generate shell completions, probably in combination with clap_complete.