Conversion Host Enablement - Configuration Wizard - Submit VMware hypervisors SSH private key at enable time

[mturley]

Part of the Conversion Hosts UI feature BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1693339

Originally part of #855, I'm disabling this field in the UI until the back end support is ready.

I don't think we can release the Conversion Host settings page without this support.

This issue is for the second of these two SSH keys collected in the Authentication step of the wizard (VMware hypervisors SSH private key):

The other SSH key is tracked separately in #898.