[BUG] Forgot Username/Email feature

[hrauniya]

Describe the bug
No email notification of forgotten username sent when "Forgot Email" feature used with phone number submission, endpoint for feature missing

To Reproduce
Steps to reproduce the behavior:

1. Register with NPDC, and log out OR
2. Click on Forgot Password --> Forgot Username, Fill phone number field, and submit
3. Wait for forgotten username email notification

Expected behavior
When the Forgot Username button is clicked, the expected behavior is to receive an email notifying the user of their respective username/email.