Revise mUzima form discrimnator from html-registration to json-registration

Currently, we have two main naming convention for discriminators - json and xml. In order to be consistent, need to revise html-registration to json-registration.

As a developer, I want to follow the naming convention for mUzima form discriminator so that it avoids any confusion for other developers.

Acceptance Criteria

• Rename html-registration to json-registration
• Download form with json-registration discriminator,
• Register and save new patient on device,
• Upload registration data to server,
• Successfully process the data on server.