Add systemTimeSource property in response of EBT

:Release Notes:
getEffectiveBroadcastTime also returns systemTimeSource if system-wide
time used for response.

:Detailed Notes:
getEffectiveBroadcastTime now also returns systemTimeSource to
indicate that we're providing time obtained from system-wide time and
synchronized with that particular time source. In case if we have
broadcast time and return it we omit that property in response.

:Testing Performed:
tested getEffectiveBroadcastTime request on desktop build

:QA Notes:

:Issues Addressed:
[GF-58477] Need information about source of getEffectiveBroadcastTime

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Change-Id: I0fb4772e59e83207ea9c1d34f34cf0fb31f31ac5
Reviewed-on: https://g2g.palm.com/4387
Reviewed-by: DCO Verification
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Reviewed-by: Andrii Zora <andrii.zora@lge.com>
Reviewed-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Tested-by: Alexandr Smoktal <alexandr.smoktal@lge.com>