Format all files with prettier VSCode plugin and add yamllint in CI (#413)

@justusbunsi to end my formatting mess... ;)

I am not fully sure myself about the linebreaks in `values.yaml` but I don't think there's an easy way to change that behavior.

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/413
Reviewed-by: justusbunsi <[email protected]>
Co-authored-by: pat-s <[email protected]>
Co-committed-by: pat-s <[email protected]>

unittests/statefulset/basic.yaml

@@ -12,6 +12,6 @@ tests:
       - hasDocuments:
           count: 1
       - containsDocument:
-          kind: StatefulSet  
+          kind: StatefulSet
           apiVersion: apps/v1
           name: gitea-unittests