Application-level TEA redirects

[ppkarwasz]

In the meeting we discussed using the PURL repository_url qualifier to locate a TEA server. The downside: this assumes each package repository runs a TEA service for millions of packages, which is unlikely.

As an alternative we could allow allow TEA endpoints (especially productReleases) to include redirects to external TEA servers, for example by allowing special link objects in the response alongside normal productRelease objects.

This would let package repositories support TEA at minimal cost by simply redirecting requests to the TEA servers operated by individual package owners.