Update http error code when datasource health check fails (#37895) (#37914)

Since the datasource settings are configured by the user, the health check error could be a client error. A 506 error may be sufficient as well.

(cherry picked from commit db2e0d46b7)

Co-authored-by: Stephanie Hingtgen <stephanie.hingtgen@grafana.com>

pkg/api/datasources.go

@@ -477,7 +477,7 @@ func (hs *HTTPServer) CheckDatasourceHealth(c *models.ReqContext) response.Respo
 	}
 
 	if resp.Status != backend.HealthStatusOk {
-		return response.JSON(503, payload)
+		return response.JSON(400, payload)
 	}
 
 	return response.JSON(200, payload)