Implement the CreateWorkspaceBlob gRPC function to create, compress, encrypt, and retrieve Workspace BLOBs from the tf-runner.

[yiannistri]

From #911

Creating Workspace BLOB: The TF-Controller invokes a new gRPC function named "CreateWorkspaceBlob".
The content of the Workspace file system is compressed using tar and gzip to produce the Workspace BLOB.
The TF-Controller retrieves this BLOB as a byte array via the return value of the CreateWorkspaceBlob gRPC function.

Creation, compression and encryption process are done in tf-runner.

[luizbafilho]

@chanwit to clarify what needs to happen, the when calling CreateWorkspaceBlob, the tf-runner should zip the terraform.tfstate.d directory and return that as the payload?

[chanwit]

Not that dir, but the whole terraform dir that is extracted.

Basically the idea is to keep everything after code generation (vars, secrets, configmap) as a tar gz blob.