[BE] Implement Sign Up For Project Building API

[davorminchorov]

Business Requirements

As a member, I want to be able to sign up for a project so that I can connect with others and build it.

Acceptance Criteria

• There should be an endpoint which will allow members to sign up to a project (an accepted proposed proposed idea).
• The following fields should be required:
• Availability (per week: 10 hours, 20 hours, 30 hours, 40 hours, custom)
• Vocation Category
• Available dates and times
• Note
• There should be an endpoint which will allow members to cancel a project sign up.
• There should be an endpoint which will allow members to edit a project sign up (same fields above).
• This endpoint should require authentication
• There should be authorization guards to prevent other members from signing up specific members to work on a project
• There should be an API documentation for the endpoint