[Thread] Make ThreadConfiguraiton a system API

This CL adds 3 things as @SystemApi:
- The ThreadConfiguration class except the Builder nested class.
- The ThreadNetworkController#registerConfigurationCallback method.
- The ThreadNetworkController#unregisterConfigurationCallback method.

Bug: 342519412
Test: CtsThreadNetworkTestCases

Change-Id: I8d3e48b73d471af1515f251451a1259a4bde69af
9 files changed