Create StatsBootstrapAtomService

Design doc is at go/statsd-bootstrap-logging. Creates a proxy service for
logging atoms from bootstrap processes to statsd. Service has one API,
which converts StatsBootstrapAtom into StatsEvent and logs to statsd.
This should only used by processes that start in the bootstrap namespace
and cannot directly link statsd's libraries to log to statsd.

Bug: 204889815
Test: booted, made sure binder service was published.
Change-Id: I09709a30a42a7a398234c995324f62a0d62ad24f