Add Github URL validation to 'Prework Repository' on Application Form

[ayumi-b]

Description:

Brief Summary: Proposal to implement Github URL validation for the 'Prework Repository' field on the application form to reduce input errors and ensure data quality. The application form can be found here:

Field Details:

Field Name: Prework Repository
Current Behavior: Currently accepts any text input without checking for a Github url. It also allows for no input.
Required Validation: The field should validate for at least the domain name 'github.com' to be part of the input
Rationale: Adding URL validation will help prevent user errors during sign-up, and prevent applicants from inputing 'none' in the field or leaving it completely blank

Expected Behavior after Implementation: Upon entering data in the 'Prework Repository' field OR leaving the field blank and pressing 'Apply', the system should immediately check for format validity. If the input does not match the expected format, an error message will be displayed.

Error Message: "Please enter your Github Prework Repository URL. For example, github.com/jody-civilian/prework"