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Add RBAC policies for NetworkPolicy

**What this PR does / why we need it**:
When using RBAC, none of the namespace-level roles currently have permission to do anything with NetworkPolicy. (Only cluster-admin does, by virtue of having permission on "*".) This fixes it so "admin" and "edit" have read/write permission, and "view" has read-only permission.

I added permission for both the extensions and networking objects, which I believe is correct as long as both of them exist?

(This would be nice to fix in 1.9, although it's not a regression. It's always been broken.)

**Release note**:
```release-note
When using Role-Based Access Control, the "admin", "edit", and "view" roles now have the expected permissions on NetworkPolicy resources.
```