Feat: add query stac for automate cron workflow

[lhoupert]

Main Changes:

• Adds a new Python script scripts/query_stac.py that queries a STAC API to identify new items in a source collection within a configurable time window
• The script checks if items have already been processed in a target collection and outputs a JSON list of items that need processing
• Includes comprehensive unit tests (tests/unit/test_query_stac.py) with mock STAC clients covering various scenarios including error handling and edge cases
• Adds minimal JSON fixtures for reproducible testing of source and target collections

[emmanuelmathot]

Good. just using logger

[lhoupert]

Change done,

except for

    # Output ONLY JSON to stdout (for Argo withParam)
    sys.stdout.write(json.dumps(items_to_process))
    sys.stdout.flush()

as I need this in the standard output so Argo can parse it here:
https://github.com/EOPF-Explorer/platform-deploy/blob/7e817c4451e625fcfdd48ee015a9816c8c6ab0af/workspaces/devseed-staging/data-pipeline/cronwf/eopf-explorer-cronwf-recent-data-processor.yaml#L85