Add login.gitter.im CNAME DNS records

Add the following CNAME DNS records to gitlab-com AWS Route53 so the sub-domain redirects. This is aimed to address https://gitlab.com/gitlab-org/gitter/webapp/issues/2278#note_214126141

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

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I tried adding the DNS records to the Gitter troupe AWS Route53 gitter.im. hosted zone but it had no effect. And remembered that this is now handled in the gitlab-com AWS account, https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5516#note_144153986

cc @dawsmith for assigning