[Dev UI] Replace JSONSchema Faker with Custom Solution

[MichaelDoyle]

We need a good way to generate "stubbed" JSON objects for input fields. Currently we use JSONSchema Faker, but it's more geared towards "fuzzing", which we are constantly fighting against to generate stubs that meet our requirements.

• show all required fields, with a preset initial value (e.g. "", 0, false)
• preset values must respect min/max/etc constraints on the schema
• respect default values from the schema
• show optional iff they come with predefined defaults (and include the default value)