helm: adjust naming of some of the variables to match our pattern

[szaimen]

Check if we should adjust the naming of some values to match our default pattern

The default pattern is COMPONENT_OPTION. So for example NAMESPACE should probably be migrated to CHART_NAMESPACE for general settings. Also SUBSCRIPTION_KEY should probably be named NEXTCLOUD_SUBSCRIPTION_KEY and more.

Might also need to adjust some values here then: https://github.com/nextcloud/all-in-one/blob/main/nextcloud-aio-helm-chart/values.yaml

[szaimen]

Started working on it in #7196