Add Alerts tab details

[josefaworks]

As a platform operator, I can click into the Alerts tab to see a yaml file with the details of how events are filtered by severity and involved object, and what provider to use for dispatching so that I can make sure the notification is configured correctly Figma Link: https://www.figma.com/file/IVHnM9iyeFWpd11evtY8ux/Weave-GitOps?node-id=4908%3A9125