doc: Update required fields for Create Contact API

[HarishTeens]

When I was trying to create a contact through the API, I was getting Bad request response. The API docs said it would give me appropriate error messages but it didn't unfortunately. Anyway, I found out it was because I was not sending the name field in request body. It simply doesn't make sense to create a contact without a name :sweat_smile: Even though I still feel it's better to update the docs.

https://www.chatwoot.com/developers/api/#operation/contactCreate