Description of problem:

This issue: https://bugzilla.redhat.com/show_bug.cgi?id=2102078#c13

was fixed in Pulp but not Satellite as a whole, because Katello is overwriting Pulp's headers. This header overwriting code is left over from the Pulp 2 days so we can likely take it out altogether and rely on the headers that we get from Pulp.

Related code is here: https://github.com/Katello/katello/blame/master/app/controllers/katello/api/registry/registry_proxies_controller.rb#L169

We should be able to take Pulp's headers and redirect them right to the client.

The particular issue seems to be caused by the mediaType being blank in the manifest body from Pulp, where Katello then assumes that the content-type should be either 'application/vnd.docker.distribution.manifest.v1+json' or 'application/vnd.docker.distribution.manifest.v1+prettyjws'.  However, the type could be "application/vnd.oci.image.manifest.v1+json".

Also, we are parsing the result as JSON, which should also be removed. It is unnecessary if we're simply redirecting Pulp's request. 

Version-Release number of selected component (if applicable):

All Pulp 3 Satellite

See https://bugzilla.redhat.com/show_bug.cgi?id=2102078 for more details.

This BZ blocks https://bugzilla.redhat.com/show_bug.cgi?id=2102078 !