OPENTHREAD_CONFIG_TX_QUEUE_STATISTICS_ENABLE macro

@def OPENTHREAD_CONFIG_TX_QUEUE_STATISTICS_ENABLE Define as 1 to enable TX queue time-in-queue statistics collection feature. When enabled, histogram of the time-in-queue of messages in the transmit queue is collected. The time-in-queue is tracked for direct transmissions only and is measured as the duration from when a message is added to the transmit queue until it is passed to the MAC layer for transmission or dropped. The histogram data consists of number of bins, each representing a range of time-in-queue values. The bin interval length is specified by the `OPENTHREAD_CONFIG_TX_QUEUE_STATISTICS_HISTOGRAM_BIN_INTERVAL` configuration, and the maximum tracked interval is given by the `OPENTHREAD_CONFIG_TX_QUEUE_STATISTICS_HISTOGRAM_MAX_INTERVAL`. Along with histogram, the maximum observed time-in-queue is also tracked.