New example for a data playground Terraform setup (#655)

* Initial commit for adding a sample data playground

* Update README

* Add license boilerplate to variables.tf

* Apply linting rules

* rename var to ptoject_id, create prefix var, remove extra zone var

* Adds the option for using an existing project by default

* Bundles all VPC related variables in a single vpc_config variable of type object

* Add encryption_key usage example + policy_boolean

* Add tests, apply linting and todos for upcoming PRs

* Update variables in readme

* Fix formatting via fmt

* Rename test dir to fix module conflict issue

* Add high level diagram and sort vars/outputs by alphabetical

* Modify diagram and update main README under data examples with link / summary

* Line break

* Use png in diagram

Co-authored-by: Ludovico Magnocavallo <ludomagno@google.com>

.gitignore

@@ -31,3 +31,4 @@ fast/stages/**/globals.auto.tfvars.json
 cloud_sql_proxy
 examples/cloud-operations/binauthz/tenant-setup.yaml
 examples/cloud-operations/binauthz/app/app.yaml
+env/