test: Mock server for testing (#1213)

* This test makes a call to the mock server

This will be useful for debugging grpc issues.

* Now the test works with the mock server in repo

This mock server will be super useful for ensuring that the right data gets transmitted in private preview so that we can confirm the client library is working correctly.

* Delete js file

We use the ts file instead.

* Add a README and guiding steps inline

* Simplify the instructions

* minor corrections

* Resolve linting issues

* Add headers for new code

* Skip a mock server test