'oc adm upgrade channel ...' should not clobber unrecognized spec properties

This is a clone of issue OCPBUGS-7960. The following is the description of the original issue:
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This is a clone of issue OCPBUGS-7780. The following is the description of the original issue:
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Description of problem:

4.9 and 4.10 oc calls to oc adm upgrade channel ... for 4.11+ clusters would clear spec.capabilities. Not all that many clusters try to restrict capabilities, but folks will need to bump their channel for at least every other minor (if their using EUS channels), and while we recommend folks use an oc from the 4.y they're heading towards, we don't have anything in place to enforce that.

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

4.9 and 4.10 oc are exposed vs. the new-in-4.11 spec.capabilities. Newer oc could theoretically be exposed vs. any new ClusterVersion spec capabilities.

How reproducible:

100%

Steps to Reproduce:

1. Install a 4.11+ cluster with None capabilities.
2. Set the channel with a 4.10.51 oc, like oc adm upgrade channel fast-4.11.
3. Check the capabilities with oc get -o json clusterversion version | jq -c .spec.capabilities.

Actual results:

null

Expected results:

{"baselineCapabilitySet":"None"}