Start aconfigd_system processes in init.rc

aconfigd_system is replacing aconfigd. Which one executes is toggled
by RO flag enable_system_aconfigd_rust, introduced in https://android-review.googlesource.com/q/topic:%22switch-to-aconfigd-system%22.

Bug: 378079539
Test: m
Change-Id: I6a04c38e9ef22da2b230046ddace73d6f7e39652