feat(pipeline): implement ML pipeline end to end

[mrzzy]

Motivation

Part of #6

Contents

Functionally completes ML pipeline:

• adds from_*() factory methods to convert between Congestion, Rating & TrafficImage
• extends TrafficImage to add processed_on, model_id fields needed by Rating.

Refactors:

• reverts API client to previous implementation as the current done is missing fields from the API.
• update API client to support TrafficImage.
• update tests to use old API client.

Fixes:

• Missing GCP project ID in DatabaseClient by hardcoding project ID.