Allow add webinar registrant fields

Currently the Add registrant to webinar route only accepts the name and email fields unless a workaround is performed in order enable the rest of the fields in the docs.

On our end, this requires developer intervention for each webinar created so that the add registrant route correctly accepts the data from our sign up form.

I would like to request that this route operate as the docs indicate it should, accepting the following fields without an additional PATCH call to webinar question update.

		"email": "sjfkghdsg@someemail.dfgjd",
		"first_name": "Jill",
		"last_name": "Chill",
		"address": "dsfhkdjsfh st",
		"city": "jackson heights",
		"country": "US",
		"zip": "11371",
		"state": "NY",
		"phone": "00000000",
		"industry": "Food",
		"org": "Cooking Org",
		"job_title": "Chef",
		"purchasing_time_frame": "1-3 months",
		"role_in_purchase_process": "Influencer",
		"no_of_employees": "10",
		"comments": "Looking forward to the Webinar",
		"custom_questions": [
				"title": "What do you hope to learn from this Webinar?",
				"value": "Look forward to learning how you come up with new recipes and what other services you offer."