Machine Learning - Simplify subnet definition

[SenthuranSivananthan]

Is your feature request related to a problem? Please describe.
Remove the requirement for oz, paz, rz and hrz subnets as they are more representative of the zones. Since this is a specialized archetype that deploys machine learning components, we will leave the named subnets (such as sqlmi, private endpoints, etc. in place) so that services can be deployed into each by the archetype.

This change reduces the # of required subnets by 4.

The subnets that will be defined are:

• SQL MI (delegated subnet for SQL Managed Instances) - Restricted Zone
• Databricks Public (delegated subnet for Databricks) - Restricted Zone
• Databricks Private (delegated subnet for Databricks) - Restricted Zone
• Private Endpoints (used for all private endpoints) - Restricted Zone
• AKS - App Zone
• App Service (delegated subnet for App Service) - Public Access Zone