Description

This PR follows best practices for upgrading DAGs from Airflow 1 to Airflow 2. Changes included:

• Adding an additional conftest.py to the blogs folder. For now, that DAG will stay at using Airflow 1.0, and we need to initialize a compatible DB for those tests separate from the workflows DB.
• Use of the newly released unit test util in workflows/requirements-test.txt
• Imports changed from contrib to providers
• Removal of samples that showcased running Python 2 code
• Referring to the officially supported Airflow constraints file instead of the piecemeal one I had
• Making the appropriate changes on anything previously throwing a Deprecation Warning (i.e. bash_operator -> bash)

If you would like access to my Composer environment to see the DAGs deployed, please let me know. Otherwise, here is a screenshot showing successful dag runs across the board

Fixes #5171
DataflowTemplateOperator tutorial update in CL/371792521 - removed instructions for setting gce_region Airflow variable (@sofisl )

CHANGE NOT ADDRESSED - I need to look further at the DAG example we have triggered by GCF. That will be addressed in an upcoming PR.

Note: It's a good idea to open an issue first for discussion.

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.6 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• Please merge this PR for me once it is approved.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample