Add DASH ENI HA operational flow owner attribute (#2281)

This ENI attribute is supported in the DPU driven HA mode of operation
and indicates which of the HA paired DPUs is the operational owner
for flows belonging to the ENI. The operational owner can be different
from the configured HA owner in case of HA failover.

Author: mukeshmv

experimental/saiexperimentaldasheni.h

@@ -565,6 +565,14 @@ typedef enum _sai_eni_attr_t
      */
     SAI_ENI_ATTR_DASH_ENI_MODE,
 
+    /**
+     * @brief HA flow ownership operational status
+     *
+     * @type bool
+     * @flags READ_ONLY
+     */
+    SAI_ENI_ATTR_IS_OPERATIONAL_HA_FLOW_OWNER,
+
     /**
      * @brief End of attributes
      */