Support OCI images

[everflux]

To support OCI images it seems that (at least) the http accept hader should contain application/vnd.oci.image.manifest.v1+json

Otherwise the tag is shown in craneoperator, but clicking on it results in 404 while the registry logs

time="2021-09-11T10:59:25.384746903Z" level=error msg="response completed with error" err.code="manifest unknown" err.message="OCI manifest found, but accept header does not support OCI manifests" go.version=go1.11.2 http.request.host="registry:5000" http.request.id=d7480f19-ed91-4fd2-8670-cb996547745a http.request.method=GET http.request.remoteaddr="10.40.0.59:54704" http.request.uri="/v2/nbs/storybook/manifests/a259bf4?" http.request.useragent= http.response.contenttype="application/json; charset=utf-8" http.response.duration=26.358985ms http.response.status=404 http.response.written=122 vars.name="nbs/storybook" vars.reference=a259bf4