floss: Add missing build dependency

The newly added system/gd/metrics depends on
//bt/system:libbt-platform-protos-lite, so this adds that dependency to
gd_default_deps as this is a common gd dependency.

Bug: 206079217
Tag: #floss
Test: Build Floss on Linux from empty: ninja
obj/bt/system/gd/metrics/BluetoothMetricsSources.counter_metrics.o

Change-Id: I160426fa2cfcffc272e6301cfe7650216a98c0e8