[BackEnd] Email already exist

[NikhilSharma03]

Description

** Issue **

• In the current Teacher and Student sign-up methods, it is not being checked whether the provided email already exits or not.
• This will lead to duplicate emails for multiple account.

** Required Changes **

• Check whether the email already exists or not.
• If not, then proceed with the email
• If yes, return error with message "Email already exits"

Note For Reviews

• Would love to work on it.

[ShwetKhatri2001]

Its being checked already based on error code we get for saving new document having duplicate email .

[NikhilSharma03]

Its being checked already based on error code we get for saving new document having duplicate email .

Ok i guess we can use that.