Bash autocompletion

[eprovst]

Description

For the Linux build bash autocompletion for subcommands should be included. This is unfortunately not supported on macOS and Windows.

Work to be done

• [x] Switch to CLI library that supports autogeneration of bashcompletion.
• [x] (Auto)generate completion files on build.
• [x] Include in snapcraft build config.

[eprovst]

Too much trial and error, but it works!