Create a test Airflow DAG from housing.py

[marov]

As a first step towards #236 we will create the cli command that does the following:

• Extract an executable snippet from housing.py using slicing and save as a py file
• Add Airflow specific code to that file
• Make sure Airflow test passes

[yifanwu]

For the slice we can start with the following "internal APIs" currently used in cli.py

artifact = db.get_artifact_by_name(slice)
sliced_code = get_program_slice(graph, [cast(LineaID, artifact.id)])

Also we should be concrete about what the user experience would be. We can have something like the following, with 'p value' being the example from housing.py.

# loading the slice from db
lineapy --airflow 'p value'
# loading the slice only from the runtime
lineapy tests/housing.py --airflow 'p value'

I'm leaning towards supporting the first case lineapy --airflow 'p value' and decoupling the execution from the workflow deployment, and it's supported by the python code snippet I included earlier. We should add tests though to check for the db retrieval (per @saulshanabrook's hygiene check!)