Add example of KSUpackage for crossplane

Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>

ksupkgs/crossplane/manifests/crossplane-helmrelease.yaml

+---
+# Helm release for controller
+apiVersion: helm.toolkit.fluxcd.io/v2beta1
+kind: HelmRelease
+metadata:
+  name: crossplane
+  namespace: crossplane-system
+spec:
+  chart:
+    spec:
+      chart: crossplane
+      reconcileStrategy: ChartVersion
+      sourceRef:
+        kind: HelmRepository
+        name: crossplane-stable
+        namespace: crossplane-system
+  install:
+    createNamespace: true
+  interval: 30s
+  releaseName: crossplane
+  targetNamespace: crossplane-system

ksupkgs/crossplane/manifests/crossplane-helmrepo.yaml

+---
+apiVersion: source.toolkit.fluxcd.io/v1beta2
+kind: HelmRepository
+metadata:
+  name: crossplane-stable
+  namespace: crossplane-system
+spec:
+  interval: 30s
+  url: https://charts.crossplane.io/stable

ksupkgs/crossplane/templates/crossplane.yaml

+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: crossplane-controller
+  namespace: crossplane-system
+spec:
+  interval: 1h
+  retryInterval: 1m
+  timeout: 5m
+  sourceRef:
+    kind: GitRepository
+    name: sw-catalogs
+    namespace: flux-system
+  path: ./infra-controllers/crossplane/controller/manifests
+  prune: true

ksupkgs/crossplane/templates/namespace.yaml

+apiVersion: v1
+kind: Namespace
+metadata:
+  name: crossplane-system
+