Move samples over to using flask instead of aiohttp

[stevengum]

Describe the solution you'd like
Move samples over to using flask

Additional context
Per the Jet Brains Python Developers Survey for 2018, 47% of developers are using Flask with a 15% increase in usage.

Additionally, most of the Azure documentation for deploying Python websites to Azure are using Flask (e.g. Linux App Service via VS Code)

[enhancement]