GitLab

See https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6601
for more information

This will make our workflow clearer and won't require a full updade
(with `tf get -update`) to update module sources

Alertmanager only needs 20MiB of ram, reduce allocation from 30G to
3.75G. Saves ~$850/month.

* Addresses: https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/4869

Resizing prometheus-app data disk for https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5997

* Uses a one-off style module since this node is temporary, there is no
reason to muck with the sidekiq module

Deploy Process
* Ensure the chef role has been applied
* Run terrafrom apply
* Validate the server is ready

* These nodes were manually removed, so terraform wants to build them
* Some items were left behind, so terraform must be run after this is
merged
  * I would highly recommend targeting `module.postgres` as other
  changes want to be made unfortunately
* Cleans up the naming for consistency with patroni while we are at it

* Closes: https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5831

* These nodes are no longer serving their purpose
* Does _NOT_ remove the pubsub nodes for geo
  * This requires all pubsubs to be recreated due to the way that module
  was written 😒

This is needed in order to make sure we have enough room on /tmp where
wal-e prepares data.

This reflects the actual capacity need closer.

Closes https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5566.