Allow users to receive the connection event counter and timestamp

This new feature enables user applications to register to receive timestamps for anchor points and connection event counters for specific or all connection events. The timestamp of the anchor points provides a time reference for the user application (i.e. to kick off an application task at the beginning of each connection event).

This is done using the Gap_RegisterConnEventCb API to register for a connection event callback. For more details, refer to the BLE5-Stack User's Guide (Navigate to the following section: BLE5-Stack-> Generic Access Profile (GAP) > GAP Connection State)