Add ability to cache ETL data sources (#2169)

* Add a rough prototype allowing a developer to pre-download data sources for all ETLs

* Update code to be more production-ish

* Move fetch to Extract part of ETL
* Create a downloader to house all downloading operations
* Remove unnecessary "name" in data source

* Format source files with black

* Fix issues from pylint and get the tests working with the new folder structure

* Clean up files with black

* Fix unzip test

* Add caching notes to README

* Fix tests (linting and case sensitivity bug)

* Address PR comments and add API keys for census where missing

* Merging comparator changes from main into this branch for the sake of the PR

* Add note on using cache (-u) during pipeline

data/data-pipeline/data_pipeline/tests/sources/national_risk_index/test_etl.py

@@ -36,23 +36,12 @@ class TestNationalRiskIndexETL(TestETL):
 
     def test_init(self, mock_etl, mock_paths):
         """Tests that the mock NationalRiskIndexETL class instance was
-        initiliazed correctly.
-
-        Validates the following conditions:
-        - self.DATA_PATH points to the "data" folder in the temp directory
-        - self.TMP_PATH points to the "data/tmp" folder in the temp directory
-        - self.INPUT_PATH points to the correct path in the temp directory
-        - self.OUTPUT_PATH points to the correct path in the temp directory
+        initialized correctly.
         """
         # setup
         etl = NationalRiskIndexETL()
-        data_path, tmp_path = mock_paths
-        input_csv = (
-            tmp_path / "NationalRiskIndexETL" / "NRI_Table_CensusTracts.csv"
-        )
 
         # validation
-        assert etl.INPUT_CSV == input_csv
         assert etl.GEOID_FIELD_NAME == "GEOID10"
         assert etl.GEOID_TRACT_FIELD_NAME == "GEOID10_TRACT"
         assert etl.NAME == "national_risk_index"