Update the "prepareSubnet.ps1" script to match the latest SQL MI Networking Requirements

The prepareSubnet.ps1 script has been used in many deployments to automate the complex networking configuration for SQL MI for about 1 year or more.

Recently it seems the SQL MI connectivity requirements have changed and some configuration has been deprecated:

https://docs.microsoft.com/en-us/azure/azure-sql/managed-instance/connectivity-architecture-overview

"[Deprecated] Network requirements without service-aided subnet configuration
Deploy SQL Managed Instance in a dedicated subnet inside the virtual network. The subnet must have these characteristics:"

Particularly, the legacy prepareSubnet.ps1 script removes service endpoints from the subnet, while it appears that recently SQL MI subnets allow service endpoint configuration.

Therefore, it appears the script needs to be updated to implement the latest connectivity requirements, in particular, not removing service endpoints configured on the subnet.

Start by reading prepareSubnet.ps1 and the linked Azure SQL Managed Instance connectivity architecture requirements. Trace where the script removes subnet service endpoints and compare that behavior with the current requirements. Done means the script no longer removes permitted service endpoints and matches the documented networking configuration.