The extensionProviders field is currently directly in SMCP.spec. In upstream, this field is under meshConfig. We're now also adding the discoverySelectors field from meshConfig.

If we end up adding other fields, the SMCP.spec may become disorganized. Also, if we end up supporting the full meshConfig field, we'll most likely expose it as SMCP.spec.meshConfig. So, we'll end up with two locations where users can specify extensionProviders or discoverySelectors - in the SMCP.spec directly, and within SMCP.spec.meshConfig. To prevent this, it makes sense to create the SMCP.spec.meshConfig field now, but have it contain only extensionProviders and discoverySelectors. If we later support other meshConfig fields, we can add them here. And if we decide to support the entire meshConfig, we'll end up with a clean SMCP spec with no duplication.