Implement direct KRM types, identity, and generate.sh for NotebookRuntime

This commit implements the direct KRM types, custom template references,
and identity configuration for NotebookRuntime (as VertexAINotebookRuntime),
fully conforming to the Greenfield resource guidelines.

It includes:
- Updating generate.sh to include VertexAINotebookRuntime.
- Defining spec and observed state fields for VertexAINotebookRuntimeSpec.
- Implementing the NotebookRuntimeTemplateRef type and normalization.
- Implementing VertexAINotebookRuntimeIdentity with FromExternal/String format.
- Adding handwritten mapper for NotebookRuntimeTemplateRef to bridge conversion.
- Passing unit tests and registering with the CAI and gcpurls registries.

Fix: 11122

Author: lovelace-coder-bot

.gemini/skills/kcc-direct-greenfield-types-implementer/journal/VertexAINotebookRuntime.md

@@ -0,0 +1,15 @@
+# VertexAINotebookRuntime Greenfield Types Implementation Journal
+
+## Observations & Design Choices
+
+1. **Mapping to GCP Resource**:
+   - `NotebookRuntime` is a resource of `aiplatform.googleapis.com` (Vertex AI API). Following the established naming pattern under `apis/aiplatform/v1alpha1`, we mapped this to the KCC Kind `VertexAINotebookRuntime:NotebookRuntime`.
+
+2. **Handwritten Mapper Support for References**:
+   - Because `NotebookRuntime` requires a template reference during assignment, we defined `NotebookRuntimeTemplateRef` in its own file `vertexainotebookruntime_reference.go`.
+   - The code generator maps `notebook_runtime_template_ref` in proto to our custom Go type but expects handwritten mappers `NotebookRuntimeTemplateRef_FromProto` and `NotebookRuntimeTemplateRef_ToProto` to avoid generation errors.
+   - We created `notebookruntime_mapper.go` under `pkg/controller/direct/aiplatform/` to bridge this conversion.
+
+3. **Verification**:
+   - Built the packages and ran unit tests to ensure `VertexAINotebookRuntimeIdentity` parses and formats the GCP resource URL (`projects/{project}/locations/{location}/notebookRuntimes/{notebookRuntime}`) successfully.
+   - Verified that the `gcpurls` registration tests successfully validate our newly added identity template.

apis/aiplatform/v1alpha1/generate.sh

@@ -30,7 +30,8 @@ go run . generate-types \
     --resource VertexAISpecialistPool:SpecialistPool \
     --resource AIPlatformModel:Model \
     --resource VertexAIFeatureOnlineStore:FeatureOnlineStore \
-    --resource VertexAITuningJob:TuningJob
+    --resource VertexAITuningJob:TuningJob \
+    --resource VertexAINotebookRuntime:NotebookRuntime
 
 # Post-process types.generated.go to inject kubebuilder validation annotations for recursive self-referential fields
 python3 -c "