Make Provider and Region configurable for Acc Tests

[albrechtflo-hg]

In the acceptance test for Clusters (and potentially also in the one for Connectors, see #82), the Cloud provider and region to use for the cluster are encoded directly into the terraform config to use.

As e.g. we are tied to one specific cloud provider with our Confluent Cloud instance (hint: not AWS), I had to locally adjust the test files to be able to run the Acceptance Test, and rollback these changes after successful testing.

If these two parameters were also configurable for the Acc Tests, one could run the Acc Tests more easily - also e.g. in one's own GitHub Fork.