Docker tests

Add tests which builds a docker container using the dotnet isolated image, run it and validate basic functionality.

The docker repo has tests but the function app payload it uses does not get updated often. It makes sense for us to build this in to our CI.

Review the existing tests in the Docker repository and this project's CI configuration to understand how container tests and function app payloads are handled. Add coverage that builds a container from the .NET isolated image, runs it, and validates basic functionality in CI; done means the test passes against the current function app payload.

Written by the indexing model from the issue text.