Cannot test applications with `.` in their name

Running the argocd-notifications binary to test template is impossible when the application name contains a `.` in its name.

```
kubectl exec -it argocd-notifications-controller-744b5d8868-84xh4 -- /app/argocd-notifications template notify app-sync-succeeded my.application.name
failed to load resource: open my.application.name: no such file or directory
```

### Problem

When the RESOURCE_NAME contains a `.`, it is assumed it's a file.

https://github.com/argoproj/notifications-engine/blob/e8ac53e2f18eb747a7173f12c818bfc6182688bb/pkg/cmd/template.go#L58

Start in pkg/cmd/template.go at the linked line and reproduce the kubectl exec command using an application name containing dots. Check how RESOURCE_NAME is loaded, then verify that dotted application names are treated as resource names rather than file paths and that the reported template command succeeds.

Written by the indexing model from the issue text.