Add IaC and automation for management of Elastic Cloud
There exists a [Terraform provider](https://registry.terraform.io/providers/elastic/ec/latest/docs) and a [REST API](https://www.elastic.co/guide/en/cloud-enterprise/current/ece-restful-api.html) to manage our Elastic Cloud account and deployments therein. There is a non-trivial amount of work involved in utilizing both/either to good effect, so we need to do some high-level breakdown/planning of the individual tasks involved, and create follow-on epics/issues to "go do the thing."
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