[compare] Helm preview default namespace does nothing

[WitoDelnat]

Describe the bug

It's actually intended behaviour as "set default namespace" only overrides the namespace if its not specified. If the namespace is set to default then we wont be overwritten.

Though now while trying it out it does not feel right. I'd argue that in most cases you don't even want to deploy to default so maybe we should simply always overwrite it to make deploying Helm Previews and others easier?