ovs-offline: better allow user to choose OVS and OVN version inside the image

[amorenoz]

Compiled-in C-idl makes ovn-nbctl et.al to point to a specific ovs/ovn schema. So choosing the right OVS/OVN version inside the image can be crucial to proper debugging.

First, we should add ovn version selection to the normal build command.
But we can do better than that. An idea by @palonsoro: use an OCP release version to pin a specific OVS/OVN version tuple.

[palonsoro]

Releases have metadata indicating the commits of each of the components.

For example, for an OKD 4.11 version:

$ oc adm release info --commit-urls | grep ovn
  ovn-kubernetes                                 https://github.com/openshift/ovn-kubernetes/commit/b42cfc1afed745106a7f9674b1e884df6f2248e4