feat: rename addon vars to addon_ prefix and simplify logic in jinja templates (#1216)

Signed-off-by: Devin Buhl <devin@buhl.casa>

bootstrap/templates/kubernetes/apps/storage/volsync/ks.yaml.j2

@@ -1,4 +1,4 @@
-#% if volsync|default({}) and volsync.enabled|default(false) %#
+#% if addon_volsync.enabled %#
 ---
 apiVersion: kustomize.toolkit.fluxcd.io/v1
 kind: Kustomization
@@ -10,7 +10,7 @@ spec:
   commonMetadata:
     labels:
       app.kubernetes.io/name: *app
-  #% if longhorn|default({}) and longhorn.enabled|default(false) %#
+  #% if addon_longhorn.enabled %#
   dependsOn:
     - name: longhorn
   #% endif %#