Add managed distributed cache resource

[goncalo-rodrigues]

Distributed cache is offered among AWS, Azure and GCP.

This issue tracks the first implementation of a managed distributed cache resource, supporting Redis engine (memcached in the future), and both stand-alone and replicated servers.

GCP doesn't have Redis cluster support and Azure doesn't allow you to specify the version (which is 4.0 for now).

AWS: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/elasticache_cluster Azure: https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/redis_cache GCP: https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/redis_instance