Add Last Successful Discovery Time Field

NetBrain currently exposes a Last Discovery Time field that reflects the most recent discovery attempt for a device, regardless of whether that attempt succeeded. As a result, users cannot rely on this field to determine when a device was last successfully accessed and its data confirmed current. This enhancement proposes adding a distinct, reportable field for Last Successful Discovery Time (or Last Successful Access Time), populated only when discovery completes successfully for a device. Customers managing large device inventories would gain a reliable way to identify devices with stale or unconfirmed data, supporting more accurate reporting and targeted troubleshooting of access failures.