Group Activity - MRs Chart w/ Single Series: App skeleton

This issue includes the following tasks:

1.) Let's create a single page -- not merely set of components -- that will serve a wide variety of reporting needs. A single url such as https://gitlab.com/-/analytics/report-page/some-data-set-definition-slug will serve up the experience. The slug is an id of a Data Set Definition which defines how data is to be retrieved and rendered.

2.) Change metric titles on the Group overview page and add hyperlink to members metric (blue-700, on-hover underline)

3.) Add a back link which displays only back and will fire the browser back button so no context needs to be passed to the page. We will revisit a richer breadcrumb later.

Note: The page won't render anything yet. Adding content to the page out of scope for this issue. There's a follow-up issue in #218460 (closed)