feat: create pmtiles for new datasets + update location extraction

[cka-y]

Summary:
This PR introduces a new pipeline task system for GTFS dataset processing, focusing on creating and managing Cloud Tasks for downstream processing (reverse geolocation and PMTiles building). It adds task creation utilities, integrates them into existing batch processing flows, and refactors the PMTiles builder as an HTTP-triggered Cloud Function with updated configuration and documentation.

Expected behavior:
When the batch processing completes, two tasks are created:

1. The reverse geolocation task is created if stops.txt exists and its hash differs from the previous dataset (i.e., the file was updated).
2. The PMTiles generation task is created if routes.txt exists, its size is > 0 and < 1,000,000 bytes (~1 MB), and the hash of at least of routes.txt, stops.txt, stop_times.txt, trips.txt or shapes.txt differs from the previous dataset.

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