Gitter infrastructure updates

This issue is to track planning efforts around updating the Gitter infrastructure management & automation; this issue should lead to a new epic and/or related issues for downstream work

• Setup new Terraform repo
  • Source from here, https://gitlab.com/gitlab-com/gl-infra/gitter-infrastructure/tree/master/terraform
• Delete gitter.im. zone from troupe AWS Route53, https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5647
• Add authentication/password to MongoDB, https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5519
• Setup CI/CD for Gitter Terraform & Ansible, https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5756
• Verify AWS CloudTrail logs are enabled for all regions
• Resources to manage in Terraform (if not already)
  • VPC
  • VPC ACLs
  • Subnets
  • EC2 Autoscaling groups
  • EC2 Launch configurations/launch templates
  • Security groups
  • Route53 zones, records
  • IAM users, roles, policies
  • EBS volumes
  • S3 buckets
  • AMI images
• Setup CI/CD for packer AMI images
• Automate EC2 bootstrap and ansible provisioning
• Setup stable SSH host key for bastion node (See #5860 (moved))
• Setup stable EIP and public DNS hostname for bastion node (See #5860 (moved))
• Setup automatic certificate rotation with Certmanager for ELBs/Cloudfront