[Thread] add system API setChannelMaxPowers

The `setChannelMaxPowers` allows privilege app to set the max
power of each channel. It is going to be used for controlling the
output power of the Thread radio chip.

Bug: b/320594263
Test: atest ThreadNetworkUnitTests && atest CtsThreadNetworkTestCases

Change-Id: Ic47eccd6de2da0e6cdb8f21d5b4df156b1f11747
9 files changed