WifiConfiguration: Modify time display in toString

Use TimeUtils to format the time display fields which hold wall clock
time.
Also, use |elapsedRealTime| to calculate the time durations for the
fields which are populated using elapsedRealTime.

Bug: 77224338
Test: Unit tests
Test: 'adb shell dumpsys wifi'
Change-Id: I850ebdc3ba1f7bfb7d5137382d2feed7e551c311