DNM : Upgrade k8s libraries to v0.36.0 and Go 1.26

[sameerforge]

Description
This PR aligns kapp-controller with the latest upstream Kubernetes v0.36.0 library stack and migrates the project to the Go 1.26 runtime.

Changes & Technical Impacts
Runtime Requirement: Upstream k8s.io libraries now strictly require Go 1.26.

API Server Lifecycle: The k8s.io/apiserver framework has removed legacy StopCh signals in PostStartHookContext. The initialization logic in pkg/apiserver requires a refactor to a Context-based lifecycle.

Controller-Runtime Interfaces: The upgrade to v0.23.3 introduces signature changes in TypedEventHandler and ResourceEventHandlerRegistration (specifically the new HasSyncedChecker method), affecting reconciler stability.

Dependency Alignment: Includes updates for kube-aggregator, controller-tools, and code-generator to maintain ecosystem synchronization.

❌ Current Build Failures
The following errors were captured after the dependency bump, highlighting the specific areas requiring refactoring:

Click to expand build_errors.log

# sigs.k8s.io/controller-runtime/pkg/cache
vendor/sigs.k8s.io/controller-runtime/pkg/cache/multi_namespace_cache.go:363:9: cannot use handles (variable of struct type handlerRegistration) as "k8s.io/client-go/tools/cache".ResourceEventHandlerRegistration value in return statement: handlerRegistration does not implement "k8s.io/client-go/tools/cache".ResourceEventHandlerRegistration (missing method HasSyncedChecker)
vendor/sigs.k8s.io/controller-runtime/pkg/cache/multi_namespace_cache.go:380:9: cannot use handles (variable of struct type handlerRegistration) as "k8s.io/client-go/tools/cache".ResourceEventHandlerRegistration value in return statement: handlerRegistration does not implement "k8s.io/client-go/tools/cache".ResourceEventHandlerRegistration (missing method HasSyncedChecker)
vendor/sigs.k8s.io/controller-runtime/pkg/cache/multi_namespace_cache.go:397:9: cannot use handles (variable of struct type handlerRegistration) as "k8s.io/client-go/tools/cache".ResourceEventHandlerRegistration value in return statement: handlerRegistration does not implement "k8s.io/client-go/tools/cache".ResourceEventHandlerRegistration (missing method HasSyncedChecker)
vendor/sigs.k8s.io/controller-runtime/pkg/cache/multi_namespace_cache.go:402:17: impossible type assertion: h.(handlerRegistration)
	handlerRegistration does not implement "k8s.io/client-go/tools/cache".ResourceEventHandlerRegistration (missing method HasSyncedChecker)
# carvel.dev/kapp-controller/pkg/reconciler
pkg/reconciler/configmap_handler.go:25:14: not enough type arguments for type TypedEventHandler: have 1, want 2
pkg/reconciler/configmap_handler.go:25:54: cannot use &ConfigMapHandler{} (value of type *ConfigMapHandler) as handler.TypedEventHandler[*"k8s.io/api/core/v1".ConfigMap] value in variable declaration
pkg/reconciler/secret_handler.go:25:14: not enough type arguments for type TypedEventHandler: have 1, want 2
pkg/reconciler/secret_handler.go:25:51: cannot use &SecretHandler{} (value of type *SecretHandler) as handler.TypedEventHandler[*"k8s.io/api/core/v1".Secret] value in variable declaration
# carvel.dev/kapp-controller/pkg/apiserver
pkg/apiserver/apiserver.go:140:47: hookContext.StopCh undefined (type server.PostStartHookContext has no field or method StopCh)

Analysis of Failures:

Cache Layer: The mismatch in ResourceEventHandlerRegistration shows that controller-runtime and client-go versions in this stack have incompatible internal interfaces.

Reconcilers: The TypedEventHandler errors confirm that our reconciler signatures need to be updated to support new generic arguments.

API Server: The StopCh error is the most critical, indicating that the apiserver library has removed the legacy channel-based shutdown in favor of context.Context.