add local dev and update docs for Sling

[cnolanminich]

the Sling loader was failing in prod, and I wanted to debug it. There must have been an update to Sling between version upgrades because we needed to change the AWS_BUCKET from s3://{bucket_name}/{folder_path} (old) to just {bucket_name}. That was an env var change which is now live, but for me to figure that out I had to get the local version working. This PR adds that local support:

• updates the extras in setup.py to include dagster-embedded-elt
• adds a local duckdb target and makes local dev supportable
• updates the README.md

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Location	Status	Link	Updated
batch_enrichment		View in Cloud	Apr 09, 2024 at 08:23 PM (UTC)
data-eng-pipeline		View in Cloud	Apr 09, 2024 at 08:23 PM (UTC)
snowflake_insights		View in Cloud	Apr 09, 2024 at 08:23 PM (UTC)
basics		View in Cloud	Apr 09, 2024 at 08:23 PM (UTC)
demo_assets		View in Cloud	Apr 09, 2024 at 08:23 PM (UTC)