Support for specifying Application Installation namespace

[ahmedwaleedmalik]

What would you like to be added? / User Story:
As a KKP user, I'd like the ability to explicitly specify the namespace in which my ApplicationInstallation resource will be created. Right now, we are only allowed to specify a single namespace that then is used for both the ApplicationInstallation and application.spec.namespace.name which determines where the resources for application will be created/installed.

This makes it a bit ambiguous as it should be possible to create all the ApplicationInstallations in a single namespace irrespective of where the resources are created since they have a separate dedicated field.

[ahmedwaleedmalik]

With this feature, we should also add a field somewhere; seed, datacenter, KubermaticSettings, or KubermaticConfiguration that can store the default namespace for ApplicationInstallations. Some users might want to let's say have a dedicated namespace apps where they'd like to place their ApplicationInstallations.