Implement more powerful shell completion

[bartekpacia]

[!WARNING]

This PR is not ready by any means.

[!NOTE]

I did some research here. Still WIP.

What type of PR is this?

• feature

What this PR does / why we need it:

see discussion in #1905

Which issue(s) this PR fixes:

resolves #1905

Special notes for your reviewer:

N/A

Testing

• Unit tests
• Manual tests (to test if actually works, in real terminal)

It would be cool if we could have some automated testing for shell completion.

Release Notes

TODO