docs: clarify cluster version change impact for ClusterGenerator, CMP Plugins and migration (argoproj#26851)

Signed-off-by: reggie-k <regina.voloshin@codefresh.io>

Author: reggie-k

docs/operator-manual/applicationset/Generators-Cluster.md

@@ -152,14 +152,14 @@ spec:
   - clusters:
       selector:
         matchLabels:
-          argocd.argoproj.io/kubernetes-version: 1.28
+          argocd.argoproj.io/kubernetes-version: v1.28.1
         # matchExpressions are also supported.
         #matchExpressions:
         #  - key: argocd.argoproj.io/kubernetes-version
         #    operator: In
         #    values:
-        #      - "1.27"
-        #      - "1.28"
+        #      - "v1.27.1"
+        #      - "v1.28.1"
 ```
 
 ### Pass additional key-value pairs via `values` field

docs/operator-manual/upgrading/3.2-3.3.md

@@ -73,6 +73,26 @@ This design change improves repository cleanliness, reduces unnecessary commit n
   Review your automation workflows and repository maintenance scripts to ensure that old or unwanted files in application paths are cleaned up if necessary. Consider implementing a periodic manual or automated cleanup procedure if your use case requires it.
 - For more details on current behavior, see the [Source Hydrator user guide](../../user-guide/source-hydrator.md).
 
+### Cluster version format change
+
+**New behavior:**
+
+3.3.3 now stores the cluster version in a more detailed format, `vMajor.Minor.Patch` compared to the previous format `Major.Minor`. 
+
+This change is aligning how ArgoCD interprets K8s cluster version with how Helm `3.19.0` and above interprets it.    
+
+This change makes it easier to compare versions and to support future features. It also allows for more accurate version comparisons and better compatibility with future Kubernetes releases. 
+
+
+**Impact:**
+
+Application Sets with Cluster Generators, that fetch clusters based on their Kubernetes version and use `argocd.argoproj.io/auto-label-cluster-info` on the cluster secret, need to be updated to use `argocd.argoproj.io/kubernetes-version` with the `vMajor.Minor.Patch` format instead of the previous `Major.Minor` format. 
+More details [here](../applicationset/Generators-Cluster.md#fetch-clusters-based-on-their-k8s-version).
+
+Additionally, API, UI and CLI commands that retrieve cluster information now return the version in the `vMajor.Minor.Patch` format.
+
+The env variable $KUBE_VERSION that is used with Argo CD CMP Plugins remains unchanged and returns the version in `Major.Minor.Patch` format, so CMP Plugins are not impacted.
+
 ### Anonymous call to Settings API returns fewer fields
 
 The Settings API now returns less information when accessed anonymously.
@@ -92,8 +112,7 @@ removed in a future release.
 
 ## Helm Upgraded to 3.19.4
 
-Argo CD v3.3 upgrades the bundled Helm version to 3.19.4. There are no breaking changes in Helm 3.19.4 according to the
-[release notes](https://github.com/helm/helm/releases/tag/v3.19.0).
+Argo CD v3.3 upgrades the bundled Helm version to 3.19.4. This Helm release interprets K8s version in a semantic version format of `vMajor.Minor.Patch`, instead of the previous `vMajor.Minor` format. This led to a breaking change in Argo CD described [above](#cluster-version-format-change).
 
 ## Kustomize Upgraded to 5.8.1