Optional parameter that you can include to specify the service tier you'd like to use for requests.
'on_demand': Default.'flex': On-demand processing when capacity is available, with rapid timeouts
if resources are constrained. Provides balance between performance and
reliability for workloads that don't require guaranteed processing.'auto': Uses on-demand rate limits, then falls back to 'flex' if those
limits are exceededSee the Groq documentation for more details and a list of service tiers and descriptions.