Update the api(s) for ApplyToPlacementEvent Form

[Doraemon012]

Is your feature request related to a problem? Please describe.

We need a backend that supports dynamic form fields for different placement events. Currently, we don't have a flexible way to pass and manage event-specific fields.

Describe the solution you'd like

Create a backend that:

• Accepts dynamic fields for placement events.
• Pre-fills user profile fields (e.g., name, email, etc) and makes them non-editable.
• Handles additional required fields like academic details and resume upload.
• Eg: Application forms in platforms like unstop.

Describe alternatives you've considered

Manually creating different forms for each event, but that would be inefficient and inflexible.

Additional context

Refer to this issue, and the related PR for the forntend context,