API Endpoint: Get List of Collaborators for a Project

[vansh909]

Title: Implement API to Fetch Collaborators of a Project (Backend)

Description:
-Implement a backend endpoint to retrieve the list of collaborators for a specific project.
-Must return collaborator details (username, email, role if applicable).

Ensure only project owner or collaborators can access this info.

refers: #1179

[github-actions]

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[riyaraj-web]

assign this issue to me under GSSoC