Keep Users sidebar item active on Cohorts page

In the admin area sidebar, the "Users" navigation item did not stay highlighted when viewing the Cohorts page. The Cohorts page is served by a separate controller, and the Users menu item's active_routes only listed the users controller, not the cohorts controller.

This affected the instance admin area, and the organization admin area inherited the same problem after gaining a Cohorts page. This was an existing bug, not one created by recent changes.

Before	After

How to test

1. Ensure ui_for_organizations and org_stage_xperimental feature flags are enabled.
2. Visit the Cohorts page in the instance admin area and confirm the "Users" sidebar item stays active.
3. Org admin can't be directly tested in this MR without changes from !254514 (merged). I chose not to stack the MRs because this change can be standalone in terms of code, and it's a quick fix. I didn't want to complicate with a stack.

Related

• Follow-up to !254514 (merged)
• Related issue: #607559 (closed)