[cli] Add bash completion script, and install with Homebrew

Description

It would be nice if the CLI as installed via Homebrew had bash completion.

I've added a completion command via #213 which can be used to create a bash completion script. This can then be released and added as part of the Homebrew formula.

Note: homebrew formula is still pending due to repo age (<30 days until about June 11): Homebrew/homebrew-core#28584

Related issues/PRs

• #213