Use the same location and structure as the flatcontainer to store packages

[scottbommarito]

1. Gallery should use the same location and structure as the flatcontainer to store packages. i.e packageid/packageversion/packageid.packageversion.nupkg
2. To prevent duplication of packages in storage we should use flatcontainer as primary storage location. When uploading a package, it should be uploaded directly to flatcontainer. When downloading a package using the V2 API, the user should be redirected to the flatcontainer.

The change should include:

1. HandlePackageEdits should use the new location
2. ArchivePackages job should use the new location
3. Catalog2DNX should be modified or moved into the Gallery

Things to take into account:

1. Gallery is deployed locally by customers. They shouldn't be affected by this change, whether they store packages in file system or blob storage
2. V3 pipeline has not been verified to be completely identical to the Gallery DB. Flatcontainer might have missing packages, so we cannot swap to it and assume all packages to be present. We must scan flatcontainer before this change and verify it's completeness.
3. We need to check that no old client versions hardcode the packages container path.
4. We need to check the path is not hardcoded anywhere in our code.