Add Terraform registry manifest file

[ldhenry]

This PR adds the terraform-registry-manifest per the official documentation here:

protocol_versions: List of strings with supported Terraform protocol versions of the provider. Providers developed using Terraform Plugin SDK version 2 should set this field to ["5.0"]. Providers developed using Terraform Plugin Framework should set this field to ["6.0"] unless the Framework is explicitly configured for protocol version 5. Defaults to ["5.0"].
Given that this was not specified previously, I'm pretty sure we been using the default of 5.0 all along.

[monsagri]

makes sense to me