Form Editor: Add a target output list of keys to the form editor UI

[prestoncabe]

There should be a list of keys that the Benefit Analyst needs to account for when building the form.

The keys are compiled from the data type schemas for the library checks included, and the DMN inputs for the custom checks included.

example:

people.id // we should be able to automatically provide this behind the scenes or via form-js component
people.dateOfBirth // --> becomes situation.people.dateOfBirth when sent to the library-api
custom.livesInPhilly // 'custom' prefix used for all custom checks DMN inputs
simpleChecks.ownerOccupant // 'simpleChecks' is the prefix for library benefits simple checks (perhaps can forgo this for now if not implementing library benefits)

Extra credit: add a simple implementation for validating the form components against the needed list of keys.