Register network tracing in system_server after boot

This runs the Perfetto and NetworkTraceHandler initialization on system
initialization along with the existing NetworkStatsService. The code is
run within the context of the system_server and is only executed on U or
later devices running eng or userdebug builds.

Bug: 246985031
Test: build & flash
Change-Id: I2b091e31c3ded54c0d7062d7d73f33ed47e0bf98
5 files changed