Investigate adding bash auto-completion in urfaves new v2 implementation

[kneal]

Description

What is your idea?

After we upgrade to cli/urfave v2, we should investigate auto-completion again to make the CLI easier to use.

auto-completion docs in v2 library:
https://github.com/urfave/cli/blob/master/docs/v2/manual.md#bash-completion

Value

Why is this important? Who does it impact? Will this make something better, faster, etc?

improves usability

Definition of Done

What is the end goal of this story?

We have options for deciding if we want to move forward with auto-completion.

[jbrockopp]

Hello 👋

The Vela admins have decided to condense all existing issues into a single repo found @ go-vela/community.

For a direct link to your counterpart issue in that repo, you can find it linked yesterday in the history of this issue.

If you have any questions, please feel free to direct them to the community repo.

Thanks for your input and feedback!