NuGet - Package Content Service

Adds the three endpoints associated with the Package Content Service

Investigation issue details

Related: #20050 (closed)

This is step 7 of 7 in implementing the NuGet API MVC:

1. #36496 (closed) - API Skeleton + The Service Index + authentication
2. gitlab-workhorse#235 (closed) - Workhorse upload route
3. #36499 (closed) - Push/Delete Service
4. #36502 (closed) - Metadata extraction job, DB changes, and dependencies
5. #36504 (closed) - Package Metadata Service
6. #36505 (closed) - Search Service
7. #36506 (closed) - Package Content Service

### Technical notes

The nuget spec file endpoint, although documented, is not necessary for the MVC