Support collapsible/expandable chart groups

Problem to solve

Right now, if a group of metrics on the dashboard isn't displaying, we just see a header with no additional information about why the metric group isn't showing. As a first step, we should make these headers expand/collapse so that we can introduce a metric group empty state that gives users more information about why the group's metrics aren't appearing on their dashboard.

Intended users

Further details

Proposal

Introduce a caret in the chart group header:

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

Links / references