Unified logger for Azure ML, App Insights, and Console

[liupeirong]

This library uses a single interface to log messages and metrics to Azure ML, App Insights, and Console. It also supports dependency tracing in App Insights.

• [x] Text and metric logging for all 3 loggers are implemented.
• [x] Unit tests passed for all loggers.
• [x] Dependency tracing/spans are supported in App Insights.
• [x] Published to Test PyPI (https://test.pypi.org/project/azureml-appinsights-logger/).
• [x] Run both standalone and in Azure ML experiment.
• [x] CI/CD pipeline to automate linting, unit testing, and packaging.