Install platform-bootclasspath generated config in /system/etc.

platform-bootclasspath module generates classpaths.proto config with
the information for derive_classpath to read and parse at runtime.

See go/updatable-bootclasspath.

Bug: 180105615
Test: m && launch_cvd; presubmit / DeviceBootTest
Change-Id: I0f4b1cfce9468fd6e3377a1d7233245e30f1ea51