repos page: add explanatory tooltip to site-admin repos page

Created by: mrnugget

Should be really rare for site-admins (since authz for site-admins was only enforced on cloud v1), but still makes sense to add this).

Test plan

• N/A

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.

Created by: eseliger

Review: Approved

Merged by: mrnugget at 2022-08-24 10:36:35 UTC