OPENTHREAD_CONFIG_SRP_CLIENT_SAVE_SELECTED_SERVER_ENABLE macro

@def OPENTHREAD_CONFIG_SRP_CLIENT_SAVE_SELECTED_SERVER_ENABLE Define to 1 to enable SRP client feature to save the selected server in non-volatile settings. When enabled, the SRP client will save the selected server info by auto-start feature in the non-volatile settings and on a client restart (e.g., due to a device reset) it will select the same server when searching to discover and pick one from the Thread Network Data service entries. The server info is saved only after the host info is successfully registered with the server and if it is selected by auto-start from a network data SRP *unicast* service entry.