Drop support for System.Data.SqlClient

[andreasohlund]

Describe the suggested improvement

Is your improvement related to a problem? Please describe.

• Since we support both we can't include ship with a reference to Microsoft.Data.SqlClient making the user having to add it manually
• It doesn't support Entra ID https://learn.microsoft.com/en-us/sql/connect/ado-net/sql/azure-active-directory-authentication?view=sql-server-ver16#overview

Describe the suggested solution

Remove tests and update docs to state that we only support the new client

Describe alternatives you've considered

Additional Context

No response

[tamararivera]

This has been officially deprecated and the 4.9.0 version of System.Data.SqlClient throws build errors.