Support for updating kakoune plugins with kak-plug

[lelgenio]

Standards checklist:

• [x] The PR title is descriptive.
• [x] The code compiles (cargo build)
• [x] The code passes rustfmt (cargo fmt)
• [x] The code passes clippy (cargo clippy)
• [x] The code passes tests (cargo test)
• [x] Optional: I have tested the code myself
  • [x] I also tested that Topgrade skips the step where needed

I based this off of the vim plugin updater. unfortunately kak-plug does not seem to have a easy way of outputting it's progress and result. I do believe it's possible, but am unsure if such hacks would be welcome.