Add support for form submissions

[RaeesBhatti]

- Summary
Add support for form submissions.
Fixes: #447

- Test plan

• Run netlify dev
• Make a POST request with url encoded data

- Description for the changelog
Transform the body of POST requests with Form data to match a submission-created event in Production.

- A picture of a cute animal (not mandatory but encouraged)
🐰

[erquhart]

@fool correct if I'm wrong but you weren't looking for actual submissions here, just a successful response and trigger the form submission triggered function if it exists. The form submission itself would not be retained. Sound about right?

[fool]

yes, that was indeed my thinking, @erquhart

[RaeesBhatti]

@fool Do you have any advice on where to look for sample submission-created event payload? I need the event shape to emulate that in netlify dev.

[fool]

I don't have good examples of the payloads, aside from what is in the public doc:

https://docs.netlify.com/functions/trigger-on-events/#payload

[fool]

Would be good to get a "dump the input" function example spun up. I bet @depadiernos could write one in about 5 minutes, but it's not something I can just toss out since I'm no javascript pro