Support of Azure AD token authentication

[denisbredikhin]

Azure SQL proposes several authentication methods:
https://docs.microsoft.com/en-us/azure/azure-sql/database/authentication-aad-configure?tabs=azure-powershell#using-an-azure-ad-identity-to-connect-from-a-client-application

some of them just require connection string modification.
But for Azure AD token authentication we need fill AccessToken field of SqlConnection.
Please provide some event handlers that we can use to fill in this field on every connection creation.

[alex-kulakov]

The connected and merged PR provides access to connection and you will be able to fill AccessToken property of SqlConnection