Change folder structure to support several training pipelines and models

[sbaidachni]

to bring a new model you need to:

• create a folder that is similar to diabetes_regression one
• duplicate and modify all the yaml files that start with diabetes_regression in .azure_pipelines folder
• create your own _build_train_pipeline.py that is similar to diabetes_regression_build_train_pipeline.py. Include your pipeline definition here.

related #137

[dtzar]

@sbaidachni sorry, I wish I would have thought of this / added comment during your PR. 
Could you please add another PR which adds to the code document?

1. visual structure

│   .env.sample
│   .gitignore
├───docs
├───infrastructure
│   ├───ci-cd

1. Actual steps needed to add multiple projects to the code repo in its own section of the md doc