Setup CI/CD for Gitter Terraform & Ansible

Part of https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5493

We have some experience now running ansible in CICD which is done for the patcher pipeline, it would be nice to set this up on the ops instance for gitter.

• Come up with a repository name
• Design the pipeline workflow

Note that for GitLab.com we are utilizing a system account for ssh that is restricted to the runner where ansible runs, this is something we could do as well for Gitter.

/cc @ctbarrett