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/default/kustomization.yaml.j2

@@ -3,9 +3,9 @@ apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:
   - ./namespace.yaml
-  #% if homepage|default({}) and homepage.enabled|default(false) %#
+  #% if addon_homepage.enabled %#
   - ./homepage/ks.yaml
   #% endif %#
-  #% if discord_template_notifier|default({}) and discord_template_notifier.enabled|default(false) %#
+  #% if addon_discord_template_notifier.enabled %#
   - ./discord-template-notifier/ks.yaml
   #% endif %#