fix: private helm registry (#7)

Fixing the setup for the private helm registry. Instead of providing the "host" as the name of the field would suggest, one has to provide a full URL, which also becomes clear, when reading the [documentation](https://docs.renovatebot.com/getting-started/private-packages/).

Reviewed-on: #7
Reviewed-by: branch-buddy <branch-buddy@t00n.de>
Co-authored-by: Timo Behrendt <t.behrendt@t00n.de>
Co-committed-by: Timo Behrendt <t.behrendt@t00n.de>

helm.json

@@ -16,7 +16,7 @@
   },
   "hostRules": [
     {
-      "matchHost": "gitea.t000-n.de",
+      "matchHost": "https://gitea.t000-n.de/api/packages/t.behrendt/helm",
       "hostType": "helm",
       "username": "{{ secrets.HELM_REGISTRY_USER }}",
       "password": "{{ secrets.HELM_REGISTRY_PASSWORD }}"