Rename namespace resource

[sboschman]

Description of your changes

Rename the Namespace resource to RancherNamespace to avoid k8s issue #97397

Fixes #6 Requires #7 to be merged first as this PR build on top of it.

I have:

• [X] Read and followed Crossplane's contribution process.
• [X] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

Running crossplane + provider locally on k3s, connecting with an upstream Rancher installation. Provisioning (and deleting) a ns in Rancher from a local XR, checking in upstream Rancher UI.