Update the Resource Budget menu

[bsctl]

Currently, the "Resource Budget" menu shows the list of Resource Quota objects. Initially, the aim of this menu was to give users a way to check the resource consumption at both namespace and tenant level. This info is derived from the annotations placed on the Resource Quota object by the Capsule Operator.

However, current implementation already provides this info in the Resource Quota objects from the standard "Resource Quota" page. The "Resource Budget" menu is now redundant. Shall we consider to remove it?

[bsctl]

@prometherion As per our discussion, we keep this menu but we need to change in scope. Instead of a per namespace view, we have to provide a per tenant view with a tenant selector instead of a namespace selector.