Create tenant repo for Loki and Thanos

With remote_write and Loki reaching the stage where we are ready to start onboarding new tenants, its prudent to create a repo as the source of truth for which tenants exist.

It should include:

• A list of tenants and their capabilities, yaml, toml are probably good choices for this.
• The appropriate CI mechanisms to provision those tenants
  • For now, use the existing basic auth mechanism and store those details in vault.
  • LokiMapper is built with this in mind.