Allow enabling filtering of group filter values

[bastilian]

The GroupFilter[0] component supports a isFilterable and onFilter property to enable a text input for filtering values in the opened group filter.

We should:

• Allow passing on isFilterable & onFilter for group filter
• If only isFilterable: true is provided a default onFilter should be passed that filters group values
• If an async function is provided the async function should be called with the filter value (? maybe).

[0] https://github.com/RedHatInsights/frontend-components/blob/master/packages/components/src/ConditionalFilter/GroupFilter.tsx#L88