Manifest Endpoints for Manifest Upload and Validation

[golharam]

This endpoint should be a stub that calls to an external URL to perform the validation, get the response and forward the response to the caller (UI).

[golharam]

And what resource will these endpoints operate on? There is currently no manifest resource for projects. I think we'll need that too?

[golharam]

Given a (s3) path to a manifest, we need an endpoint to validate the manifest and return a status on whether the manifest is valid or not and any errors.