Code insights: add dashboard delete modal

Created by: vovakulikov

Closes https://github.com/sourcegraph/sourcegraph/issues/22232

Background

This PR adds delete dashboard modal UI and delete dashboard logic.

By click on this action item, you must see a modal UI with delete UI. By click on the delete forever button you will be redirected to the dashboard owner built-in dashboard (user, org or global dashboard)

Context delete action item at the dashboard page

Dashboard delete modal UI

How to test

1. Go to /insights/dashboards
2. Create a new dashboard by create dashboard button
3. Open dashboard 3-dots context menu and pick delete actions
4. You must see delete modal
5. Delete Dashboard forever
6. See built-in dashboard and see that you don't have a deleted dashboard in dashboard select