Add RubyGems upload route

Proposal

As we implement the RubyGems package manager, we will need to support workhorse uploads through the new RubyGems specific routes.

We need to add

// Gem Artifact Repository
u.route("POST", apiPattern+`v4/projects/[0-9]+/packages/rubygems/`, upload.BodyUploader(api, signingProxy, preparers.packages)),

to the upstream routes file.