Add Leave organization action to overview page

What does this MR do and why?

This MR lets a user leave an organization directly from the organization overview page. A new "Leave organization" action appears under a vertical ellipsis dropdown and opens a confirmation modal warning that the user will lose access to the organization's groups and projects.

Screenshots or screen recordings

How to set up and validate locally

1. Sign in as a user who is a member of more than one organization.
2. Visit an organization overview page for an organization that is not your home organization.
   • Click organization dropdown from the top let corner.
   • Click the current organization.
3. Open the vertical ellipsis dropdown.
4. Click "Leave organization".
5. Confirm in the modal, and verify you are redirected to the dashboard with a success alert.

References

• Related to #608253 (closed)