Add stub code and tests

[exvertus]

• [x] main stubs
• [x] vscode test setup
• [x] write deploy logic
• [x] notes on pytest usage
• [x] organize tests and fixtures according to pytest best practices
• [x] review google.cloud.storage library usage
• [x] monkey-mock doc
• [x] able to run locally against cloud
  • [x] service account
  • [x] setup
  • [x] teardown
• [x] add detail to readme

[exvertus]

https://github.com/GoogleCloudPlatform/python-docs-samples/tree/main/functions/helloworld https://github.com/GoogleCloudPlatform/python-docs-samples/tree/main/functions/v2/storage https://github.com/GoogleCloudPlatform/python-docs-samples/tree/main/functions/v2/imagemagick

[exvertus]

https://cloud.google.com/functions/docs/testing/test-event