App allows a contact with more than 8 digits in the phone number to be added

[Runus01]

Description: The AddressBook app allows users to add unusually long phone numbers for contacts, potentially recording erroneous data.

Steps to Reproduce:

1. Open the AddressBook app.

2. Enter a command to add a new contact with a long phone number.

   Example command:

   add r/volunteer n/Jill p/9999999999999998765432 e/johnd@example.com a/311, Clementi Ave 2, #02-25 t/friends t/owesMoney h/30
   
   

Expected Result:
The app rejects the contact information as the phone number is longer than 8 digits as expected for Singapore phone numbers.

Actual Result:
The app accepts the contact.