Default userManagedNetworking in ACI doesn't always work

When the user is providing ZTP manifests, a missing value for userManagedNetworking (in AgentClusterInstall) should be defaulted based on the platform type - for platform None this should default to true.

This is only happening if the platform type is misspelled as none instead of None. (Both are accepted for backwards compat with OCPBUGS-7495, but they should not result in different behaviour.)

When the user starts from an install-config, we set the correct value explicitly in the generated AgentClusterInstall, so this is not a problem so long as the user doesn't edit it.