distsql, ui: query count metrics

[jseldess]

PR: cockroachdb/cockroach#17050

[jseldess]

New distributed SQL-focused metrics in the UI, @Amruta-Ranade. Not sure if you'll need to document them for 1.1. Depends on the user stories/questions you end up deciding to answer.

[jseldess]

This should be covered in Amruta's general Admin UI reference doc.

[Amruta-Ranade]

As per discussion with @couchand, not to be documented for 1.1

[Amruta-Ranade]

We are not documenting distsql for 2.0. Moving to 2.1

[Amruta-Ranade]

We are not documenting distsql yet. Punting this issue until we do.

[jseldess]

@Amruta-Ranade, will there be some engineering changes tied to our decision to document this? If so, you can close this issue and count on a future issue getting created by our release script.

[Amruta-Ranade]

I don't know yet - it depends on the scope of the "document DistSQL plans" project. And the scope of that project hasn't been defined yet. I am okay with closing this issue for now and revisiting it as and when we get to the DistSQL plans project.