[Feature Request] Remove raw payloads from WorkflowCountAggregationGroup

[chris-olszewski]

Is your feature request related to a problem? Please describe.

At the moment values are represented as payloads.

Describe the solution you'd like

I believe we should offer a search attribute list instead.

Additional context

https://python.temporal.io/temporalio.client.WorkflowExecutionCountAggregationGroup.html#group_values