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.

Inizia leggendo prepareSubnet.ps1 e i requisiti collegati relativi all’architettura di connettività di Azure SQL Managed Instance. Traccia il punto in cui lo script rimuove gli endpoint di servizio della subnet e confronta tale comportamento con i requisiti attuali. Il lavoro è completato quando lo script non rimuove più gli endpoint di servizio consentiti e corrisponde alla configurazione di rete documentata.