iOS: Use flows from mocks package for demo app

[tmarmer]

Is your feature request related to a problem? Please describe.

Managing additional mocks in the MockFlows.swift file can be a pain. Given most of the mocks have equivalents in the mocks package, having this extra file that we edit manually duplicates existing work. Additionally it only supports the JSON format of mocks and only as strings, which loses all the formatting and autocomplete advantages of the react DSL flows.

Describe the solution you'd like

Have some automation in place to make use of the mocks package in the ios demo app.

Additional context