How to add a maintainer

New maintainers are proposed by an existing maintainer and are elected by majority vote. Once the vote passed, the following steps should be done to add a new member to the maintainers team:

1. Submit a PR to add the new member to MAINTAINERS
2. Invite to GitHub organization
3. Invite to cortex-team group
4. Invite to Quay.io repository
5. Invite to Docker Hub organization
6. Submit a PR to CNCF maintainer list for Cortex
7. Invite to CNCF cncf-cortex-maintainers mailing list (via CNCF Service Desk)
8. Invite to Cortex Project Public Calendar
9. Invite to maintainer's Google Docs
10. Add to the Google Analytics property used for the website statistics
11. Invite to credentials vault