Object Storage: replace Workhorse SkipRailsAuthorizer

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Some uploads in Workhorse pass through a thing called the SkipRailsAuthorizer. This behavior is a security problem. If there is a security issue that is triggered by upload processing in Workhorse (this has happened more than once in the past), then the use of SkipRailsAuthorizer allows unauthorized users to exploit the vulnerability.

We should replace SkipRailsAuthorizer with code that calls a dedicated internal Rails API endpoint. This endpoint should check if the users is signed in.

There is a challenge here in that we currently call SkipRailsAuthorizer even if there is no upload in the request. If we do a naive replacement that would slow down the application considerably. We will have to do some refactoring to avoid the slow-down.