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/mssql/utils/utils.go

@@ -0,0 +1,28 @@
+package utils
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/grafana/grafana-azure-sdk-go/azcredentials"
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+)
+
+// GetJsonData just gets the json in easier to work with type. It's used on multiple places which isn't super effective
+// but only when creating a client which should not happen often anyway.
+func getJsonData(settings backend.DataSourceInstanceSettings) (map[string]interface{}, error) {
+	var jsonData map[string]interface{}
+	err := json.Unmarshal(settings.JSONData, &jsonData)
+	if err != nil {
+		return nil, fmt.Errorf("error unmarshalling JSONData: %w", err)
+	}
+	return jsonData, nil
+}
+
+func GetAzureCredentials(settings backend.DataSourceInstanceSettings) (azcredentials.AzureCredentials, error) {
+	jsonData, err := getJsonData(settings)
+	if err != nil {
+		return nil, err
+	}
+	return azcredentials.FromDatasourceData(jsonData, settings.DecryptedSecureJSONData)
+}