Limit to 2 alter_data_batches concurrently

[stacimc]

Fixes

Description

No limit was put on the number of alter_data batches run concurrently during the data refresh, causing Airflow to be overloaded during an image data refresh. This PR updates the DAG to allow a max of 2 concurrent alter_data batches. We can evaluate later if this can be increased (or even if it should be decreased to 1).

Testing Instructions

Run the staging_image_data_refresh DAG locally. Watch the alter_batches[] step and observe that no more than 2 tasks are put into the running state at a time.

Checklist

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