MSSQL: Add support for MI authentication to MSSQL (#73597)

* Add support for MI authentication to MSSQL

This adds support for managed identity authentication for MSSQL managed
instances running in Azure.

Co-authored-by: baldm0mma <jev.forsberg@grafana.com>

pkg/tsdb/sqleng/sql_engine.go

@@ -74,6 +74,7 @@ type JsonData struct {
 	Database                string `json:"database"`
 	SecureDSProxy           bool   `json:"enableSecureSocksProxy"`
 	AllowCleartextPasswords bool   `json:"allowCleartextPasswords"`
+	AuthenticationType      string `json:"authenticationType"`
 }
 
 type DataSourceInfo struct {