chore: add .gitignore back (#4502)

Author: Takashi Matsuo

.gitignore

@@ -0,0 +1,29 @@
+.coveralls.yml
+*.pyc
+.coverage
+.tox
+.pytest_cache
+.ipynb_checkpoints
+.executed_notebooks
+coverage.xml
+python-docs-samples.json
+service-account.json
+client-secrets.json
+__pycache__
+*db\.sqlite3
+managed_vms/django_tutorial/static/*
+**/migrations/*
+lib
+testing/resources/test-env.sh
+testing/resources/service-account.json
+testing/resources/client-secrets.json
+secrets.tar
+.cache
+junit.xml
+credentials.dat
+.nox
+.vscode/
+*sponge_log.xml
+.DS_store
+env/
+.idea