Propagate API server error metadata to GraphQL callers

[negz]

Description of your changes

This decorates GraphQL errors with a source (either the API server, or unknown). If the error comes from the API server, we bubble up the code/reason for the error, according to the API server.

I have:

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

How has this code been tested

I've tested a few failure cases to ensure we have the error extensions we expect:

Creating a Secret in a non-existent namespace:

{
  "errors": [
    {
      "message": "cannot create Kubernetes resource: namespaces \"wat\" not found",
      "path": [
        "createKubernetesResource"
      ],
      "extensions": {
        "code": 404,
        "reason": "NotFound",
        "source": "APIServer"
      }
    }
  ],
  "data": null,
  "extensions": {}
}

Creating a Bucket with no spec:

{
  "errors": [
    {
      "message": "cannot create Kubernetes resource: Bucket.storage.gcp.crossplane.io \"test\" is invalid: spec: Required value",
      "path": [
        "createKubernetesResource"
      ],
      "extensions": {
        "code": 422,
        "reason": "Invalid",
        "source": "APIServer"
      }
    }
  ],
  "data": null,
  "extensions": {}
}