Replicate Gitter webapp production terrafrom setup to beta

Currently, the only autoscaling groups that are provisioned by terraform are in the Gitter production environment.

This means that when we do changes to the terraform setup we are often forced to test those changes by deploying them straight to production. This issue is a major enabler of upgrading Ubuntu on our EC2 instances https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/7993

This issue tracks effort to replicate the terraform setup for a particular type of instances: webapp

Process

1. Create Autoscaling Group, Launch Configuration and ELB terraform config for beta webapp
   • start with copying the production config
   • replace values as appropriate by looking at the gitter-beta-01 instance
2. Validate that the beta webapp booted up correctly
3. Point the beta.gitter.im to the new webapp ELB
   • TODO: what about the WS?
4. Remove the webapp application server from gitter-beta-01