Create a tabbed navigation structure inside of Feature Flags Detail UI

Release notes

Problem to solve

The information related a single feature flag can easily become quite long, especially with many code references and strategies. This can make a single feature flag difficult to understand from it's detail view.

Proposal

Create a tabbed structure similar to MRs where a user can navigate top level information from the top of the UI.

Proposed design

Note: The numbers next to the tab labels identify the number of strategies and code references. If this number is not easily accessible, we should remove the UI moment.