Example Airflow DAG that sends an email message through SendGrid

[pavel-salnikov]

Description

Example Airflow DAG that sends an email message through SendGrid.

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

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• composer/workflows/email_operator_sendgrid.py:24, tag composer_email_operator_sendgrid

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment

[leahecole]

1. Please add a unit test - it will likely be very similar to this test
2. Should the schedule interval be daily? I can't remember, but is catchup set to True by default? If it is, this is going to run a lot when users first add it to their environments. Do you want to highlight having scheduled notifications? If not, consider having it not be scheduled and have the users trigger it as part of the tutorial
3. Run nox -s blacken and I think your whitespace lint errors will be fixed. and If they aren't, please resolve the lint failures
4. add the dependency to requirements.txt

[dandhlee]

LGTM for Python.