Add APIs to allow for a Stripe paywall to /consultation/thanks page

[otech47]

as part of #266

1. new API /consultations/generate/:consultationId

• takes the consultationId and passes it as meta into stripe.createCharge

2. new API /webhooks/stripe/generate-consultation

• we expect this payload to contain the consultationId in the metadata
• query the DB consultations table to get the description + constraints
• pass this description + constraints string into the python startup.py "<idea>" command