Add AccessToken support for Azure SQL / Fabric authentication

[swecivic-lang]

Adds optional AccessToken support to WindowsSQL tasks. When provided,
the token is applied via SqlConnection.AccessToken before opening the
connection, enabling Entra ID authentication for Azure SQL and
Microsoft Fabric Lakehouse SQL.

Changes are fully backwards compatible. Existing connection string
authentication works unchanged when AccessToken is not set.

BulkInsert now uses the existing open SqlConnection instance instead
of creating a new connection from the connection string, ensuring
the access token is preserved.

WindowsSQL.zip