Stand up API endpoint for new project requests

[matthew-li]

New project requests (excluding those for Vector for now) that have the "Approved - Processing" status can be processed programmatically, since they have been manually approved by an administrator up to that point.

Add an endpoint that supports handling of the project setup step and the final submission. In particular:

• Allow the caller to fetch a list of requests that are ready for processing.
• For these requests only, allow the caller to mark the setup step as complete and, if needed, alter the name of the project.
• Allow the caller to mark the request as processed, which will either schedule or complete the request, depending on the allocation period of the request.

Refer to (and likely refactor) the logic in coldfront.core.project.views_.new_project_views.approval_views.SavioProjectRequestDetailView.post.