[GrafanaDashboard] Use CR's namespace as a default folder name

[weisdd]

Is your feature request related to a problem? Please describe.
In v4, we used CR's namespace as a default folder name in the dashboard controller.

In v5, we use General (pre-existing folder with id 0), which contradicts the docs:

In a standard scenario, a folder with default settings gets created through a GrafanaDashboard CR. It either matches the Kubernetes namespace a dashboard exist in or spec.folder field of the CR.

Describe the solution you'd like
We should probably move back to the previous behavior to make sure we don't end up unintentionally cluttering General folder.

[NissesSenap]

So I spoke to a colleague around this and he had a good point.

It is reasonable that we should follow how grafana is working.
If you import a random dashboard and don't define a folder in the grafana UI the dashboard will be created in the General folder.

I think this is a good point, it also forces our users to perform an active decision where to put the dashboard.

What do you think around that?

[weisdd]

@NissesSenap Well, I think the previous behaviour worked great for multi-tenant environments. There, the namespace <=> folder match felt natural. Personally, I wouldn't try to match it with Grafana's behaviour.
At the same time, my intention here is only to make sure docs are not misleading, so I don't necessarily advocate for one approach or the other. :)