Filter RBAC groups with no allocations

[KashifSaadat]

As a user
I want to filter on the list of RBAC Groups created in the Platform Hub
So that I can see which have no allocations and perform some housekeeping

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Filter capabilities will be a larger piece of work to implement I suspect, and will be beneficial (for ease of use) in a lot of locations such as:

• Projects
• Services
• User / Robot Tokens
• RBAC Groups (for other attributes such as services / clusters they are assigned to)

[jits]

#231 adds this filter (and more) to the hub admin Kubernetes Groups index page.