docs: add region tag for sigterm handler (GoogleCloudPlatform#5527)

## Description

Fixes #<ISSUE-NUMBER>

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

## Checklist
- [ ] I have followed [Sample Guidelines from AUTHORING_GUIDE.MD](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md)
- [ ] README is updated to include [all relevant information](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#readme-file)
- [ ] **Tests** pass:   `nox -s py-3.6` (see [Test Environment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [ ] **Lint** pass:   `nox -s lint` (see [Test Environment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#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](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/.github/CODEOWNERS) with the codeowners for this sample

Author: averikitsch

run/idp-sql/main.py

@@ -89,6 +89,7 @@ def save_vote() -> Response:
 
 
 # https://cloud.google.com/blog/topics/developers-practitioners/graceful-shutdowns-cloud-run-deep-dive
+# [START cloudrun_sigterm_handler]
 def shutdown_handler(signal: int, frame: FrameType) -> None:
     logger.info("Signal received, safely shutting down.")
     database.shutdown()
@@ -97,11 +98,15 @@ def shutdown_handler(signal: int, frame: FrameType) -> None:
     sys.exit(0)
 
 
+# [END cloudrun_sigterm_handler]
+
 if __name__ == "__main__":
     # handles Ctrl-C locally
     signal.signal(signal.SIGINT, shutdown_handler)
 
     app.run(host="127.0.0.1", port=8080, debug=True)
 else:
     # handles Cloud Run container termination
+    # [START cloudrun_sigterm_handler]
     signal.signal(signal.SIGTERM, shutdown_handler)
+    # [END cloudrun_sigterm_handler]