[BE] Implement Accept Project Idea Proposal API

[davorminchorov]

Business Requirements

As a member, I want to be able to accept a project idea proposal so that I can start organizing the interested group of people who want to work on the project.

Acceptance Criteria

• There should be an endpoint which will allow members to accept a proposed idea for a project
• When a proposed idea is Accepted:
• the status should be changed to Accepted
• a new project should be created with title and description linked to the project idea proposal
• The status of the project should be planning
• The interested members should be notified (in-app or email, depending on their settings)
• The proposed idea should be frozen from being edited by the author, or other members being able to vote, comment, show interest etc.
• The proposed idea should return a link to the project.
• Archived proposed ideas cannot be accepted by members.
• This endpoint should require authentication
• There should be authorization guards to prevent other members from accepting the project idea of the original author
• There should be an API documentation for the endpoint