Add `cli` label for bugs and PRs?

I've seen a few issues and PRs which are solely modifying the `datafusion-cli` crate.
It would be nice for ease of finding these PRs and issues, if there was a `cli` label, or
`datafusion-cli` label that we could assign them, to make them somewhat easier to find.

Start by checking how labels are defined and managed for DataFusion issues and pull requests, then focus on the datafusion-cli crate references in the repository. Done means a cli or datafusion-cli label is available and can be assigned consistently to issues and PRs that solely modify that crate.

Written by the indexing model from the issue text.