OSTree Support

Do we need a separate ticket for delete operation?

Yes we do need a separate story for deleting repository versions. I'll open one.

@dkliban, is this how it is supposed to work (this was already added in the PR referenced in the issue https://pulp.plan.io/issues/8919)?

(pulp) [vagrant@pulp3-source-fedora33 ~]$ http :24817/pulp/api/v3/content/ostree/refsheads/?repository_version_added=/pulp/api/v3/repositories/ostree/ostree/029ee9aa-a8d6-495c-bc31-3e6b087ad28d/versions/1/
HTTP/1.1 200 OK
Access-Control-Expose-Headers: Correlation-ID
Allow: GET, HEAD, OPTIONS
Connection: close
Content-Length: 669
Content-Type: application/json
Correlation-ID: ff2dfc3ae4fc441ba98d46f546bd73d6
Date: Mon, 09 Aug 2021 22:13:43 GMT
Referrer-Policy: same-origin
Server: gunicorn
Vary: Accept, Cookie
X-Content-Type-Options: nosniff
X-Frame-Options: DENY

{
    "count": 2,
    "next": null,
    "previous": null,
    "results": [
        {
            "artifact": "/pulp/api/v3/artifacts/418b8e99-0e03-4539-9573-8773bbd1921e/",
            "commit": "/pulp/api/v3/content/ostree/commits/5ee2c6aa-45ef-44f5-8d70-8d2665d1fe77/",
            "name": "foo",
            "pulp_created": "2021-08-09T22:12:42.017004Z",
            "pulp_href": "/pulp/api/v3/content/ostree/refsheads/667e6264-ee47-4b74-af47-59d3e3dad7cd/"
        },
        {
            "artifact": "/pulp/api/v3/artifacts/adc7a405-7628-4f45-9517-70d68b44d674/",
            "commit": "/pulp/api/v3/content/ostree/commits/29ed7b20-0257-4626-ac79-33b07c6fd45d/",
            "name": "bar",
            "pulp_created": "2021-08-09T22:12:41.981642Z",
            "pulp_href": "/pulp/api/v3/content/ostree/refsheads/53d75c9b-4982-48f9-8501-84d60f7c7c59/"
        }
    ]
}