Show successful notification only when the user is registered and resets the password

### Observed Behaviour
Currently, if a user has forgotten his password he can enter the email address and a password reset link will be shared.
Even if the email address is not registered a successful notification is popped up.

### Expected Behaviour
Password reset should only be sent when the user is registered. Otherwise, display an error.

@Ram81 @RishabhJain2018

Start by tracing the password-reset flow in the Python/Django application from the email submission through its success and error responses. Confirm the behavior for registered and unregistered email addresses, and consider the work done when only registered users receive a success notification while others receive an error.

Written by the indexing model from the issue text.