Increase thoroughness of Provider conformance tests

### What problem are you facing?

This repository should define two conformance test suites; one for Crossplane distributions and another for Crossplane providers.

### How could conformance help solve your problem?

It could flesh out the provider conformance test suite, which currently exists but has no meaningful tests. We should test that:

* [x] Providers install only cluster scoped CRDs.
* [x] Providers install only CRDs that appear to be a managed resource or a provider config.
* [x] Providers install support for at least one managed resource.
* [x] All defined resources are in the "crossplane" category, and managed resources are in the "managed" category.
* [ ] A ProviderConfigUsage exists for each extant (managed resource, provider config) tuple.
* [ ] All managed resources can become 'ready'.
* [ ] All managed resources emit Kubernetes events.
* [ ] All managed resources write connection secrets (though for many these secrets would be empty).

(Edit: consolidated some of the comments below into a checklist here).