Team 030 backend arkson

[josiaharkson]

A register request body validation middleware added. To validate the firstName lastName email and userType fields from the request body.

• Checks if the above fields are empty, and returns a specific error response message.
• Checks if the email is valid
• Checks if the email already exists or has already been registered
• Checks if the userType matches enumerated user types ("cons", "ret", "farm", "inv", "who", "trans")
• Converts the email field to lowercase (since the DB does not control letter casing)
• Returns a specific explanatory error message if any field fails validation.