support priority and fairness

[nadavofi]

Pre-release doc:
https://docs.google.com/document/d/1km6GNMnAgswiyvs6tifRvxq4StXoagGfgpe0PW5fvDI/edit?tab=t.0

WorkflowService Proto file for reference: https://github.com/temporalio/api/blob/2e5751c82c13013ec7c486efb36969e56a116fe5/temporal/api/workflowservice/v1/request_response.proto#L196

Usage example:

Temporal.start_workflow(
  MyWorkflow,
  { ... },
  options: {
    priority: {
      priority: 1,
      fairness_weight: 1.0,
      fairness_key: "high",
    },
    ...
  })

[nadavofi]

tested with Temporal: