Implement Username Suggestion and Storage During User Sign-Up

[Alpha17-2]

Description

Implement functionalities to suggest and store usernames during the user sign-up process. The initial username should be a combination of the first three letters of the user's full name (excluding any white spaces) and some digits. Ensure that this username is unique by checking against existing usernames stored in the Firebase Firestore database.

Requirements

1. Username Generation:

   • Extract the first three letters from the user's full name, ignoring any white spaces.
   • Append a random or sequential set of digits to the extracted letters to form an initial username suggestion.

2. Uniqueness Check:

   • Check the generated username against the usernames stored in the Firebase Firestore database.
   • If the username already exists, modify the username by changing the appended digits and recheck until a unique username is found.

3. Storage:

   • Once a unique username is generated, store it in the Firebase Firestore database along with the user's other sign-up details.