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 <justusbunsi@noreply.gitea.io>
Co-authored-by: pat-s <patrick.schratz@gmail.com>
Co-committed-by: pat-s <patrick.schratz@gmail.com>

.markdownlint.yaml

@@ -129,12 +129,12 @@ MD041:
 MD044:
   # List of proper names
   names:
-  - Gitea
-  - PostgreSQL
-  - Memcached
-  - Prometheus
-  - Git
-  - GitOps
+    - Gitea
+    - PostgreSQL
+    - Memcached
+    - Prometheus
+    - Git
+    - GitOps
   # Include code blocks
   code_blocks: false