quay.io should go back to sending simulated signatures with Schema 1 responses to older docker clients

With the move to py3, older clients (notably 'oc' command 4.6 and earlier) may have difficulty parsing a Schema 1 manifest that does not contain a signature. Pre-py3, quay.io would add a 'fake' signature to the response so the clients would be satisfied. This is no longer the case as we are being more strict in our support for the standard.

Recommendation that quay.io go back to adding these 'fake' signatures so that older clients continue to work with quay.io (as OCP 4.6 is LTS and we cannot ask customers to upgrade).

More context:

(original issue raised on forum-quay)

https://coreos.slack.com/archives/C7WH69HCY/p1645465383807039

(eng/pm discussion)

https://coreos.slack.com/archives/G7VFPAY7Q/p1645532943917089