Add matrix.gitter.im CNAME DNS records

Add the following CNAME DNS records to AWS Route53 so the sub-domain redirects. This is currently managed in the GitLab AWS account but will soon be moved over to the Gitter troupe AWS account so we can update this.

• CNAME: matrix.gitter.im -> gitter.im
  • http://matrix.gitter.im/
  • https://matrix.gitter.im/
• CNAME: matrix-beta.gitter.im -> beta.gitter.im
  • http://matrix-beta.gitter.im/
  • https://matrix-beta.gitter.im/

Just like what we did for login.gitter.im, see https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/7871

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• Part of https://gitlab.com/groups/gitlab-org/gitter/-/epics/10 -> https://gitlab.com/gitlab-org/gitter/webapp/-/issues/1684
• The gitter.im homeserver was added to EMS in https://github.com/matrix-org/matrix-hosted/issues/2251