Lower compute costs for weather-dl

[alxmrs]

Since weather-dl is a long running, low-compute job, there's a mismatch between how much it costs to run a job (on Dataflow) vs the value it's providing. There are several options we can adopt to lower the compute costs, such as:

• Defaulting to use cheaper instances
• Using timers instead of busy waiting.
• Reconsidering Beam as the core framework of this job.