feat: add support for a dynamic form task step

[NuclearRedeye]

This PR adds initial support for defining and rendering a dynamic questionnaire form in the mobile app.

I've implemented the first 3 parts, which I'd love some feedback on. Note that the styling isn't all there but this can be cleaned up a bit later. I'm mostly after feedback on the schema and code.

I'm also looking for some input on how best to approach the final 2 parts and how best those can be implemented with an eye on the need to support a date input and currency input in the next set of stories.

Acceptance Criteria:

• Define a protobuf schema for a Form Task Step
• A a 'What's your Name' form to the KYC Task type to capture 'First', 'Middle' and 'Last' names.
• Render the form in the mobile app
• Serialise and return the form responses to the backend
• Validate user input