Add email service RPC for sendgrid domain registration

[tmthecoder]

Add email service RPC for sendgrid domain registration

Context

We need to add an RPC endpoint to interface with Sendgrid's sender domain registration API

Acceptance Criteria

• A Proto RPC with appropriate Request/Response types is generated for this RPC
• The Email Service implements the above RPC
  • This implementation should intake the parameters needed for Sendgrid domain registration (https://docs.sendgrid.com/api-reference/domain-authentication/authenticate-a-domain)
  • We need to take in the domain and subdomain (can be null) parameters
  • Return the status code from sendgrid as well as the appropriate response message (the CNAME records that sendgrid sends back)

Testing

• Please ensure there are tests written for the following cases (at a minimum):
  • Calling the rpc with a successful registration
  • Calling the roc with an unsuccessful registration