docs: add comprehensive upgrade report

Author: schegi

Makefile

@@ -2,8 +2,7 @@
 # Image URL to use all building/pushing image targets
 IMG ?= controller:dev
 # ENVTEST_K8S_VERSION refers to the version of kubebuilder assets to be downloaded by envtest binary.
-# Updated to match Kubernetes v0.33.x (Cluster API v1.11.3)
-ENVTEST_K8S_VERSION = 1.33.3
+ENVTEST_K8S_VERSION = 1.34.1
 
 # Get the currently used golang install path (in GOPATH/bin, unless GOBIN is set)
 ifeq (,$(shell go env GOBIN))