Update Crossplane GCP Bucket generation rules to use preferred API version

Modified the generation rules for Crossplane GCP Buckets to omit the version in resource type definitions, allowing the use of the API server's preferred version (currently v1beta2). Updated documentation to reflect this change and clarify version pinning for schema stability.

Changes include:
- Updated YAML generation rules to remove explicit versioning.
- Revised documentation to explain the implications of omitting versioning and the preferred version usage.

This enhances resilience across CRD upgrades and simplifies the configuration for users.

docs/04-generation-rule-walkthrough.md

@@ -14,7 +14,7 @@ spec:
   platform: kubernetes
   generationRules:
     - resourceTypes:
-        - buckets.storage.gcp.upbound.io/v1beta1
+        - buckets.storage.gcp.upbound.io
       matchRules:
         - type: pattern
           pattern: ".+"
@@ -53,9 +53,13 @@ spec:
 
 ```yaml
 resourceTypes:
-  - buckets.storage.gcp.upbound.io/v1beta1
+  - buckets.storage.gcp.upbound.io
 ```
 
+Omitting `/v1beta2` (or `/v1beta1`) tells the indexer to use the API
+server's preferred version, which survives CRD schema upgrades. Pin the
+version only when you rely on a specific schema shape.
+
 This is the *selective discovery* signal. Because this string appears in
 a loaded rule, the Kubernetes indexer knows to enumerate that CRD.
 Without any rule mentioning a CRD, it would not be listed.