cherrypick of ag/20211286

update and create bundle config pb python library

update config.pb file to the source of truth:
google3/third_party/java_src/android_appbundle/bundletool/schemas/proto/config.proto

current config.pb is stale and needs update.

Also, add a python library host soong module config_proto, so that it
can be used by other python code.

BUG: b/240288941
TETS: tested along with primary_train_build_worker that reuse
BundleConfig.pb

Change-Id: I426a5cb7ec42573ed2110494c50813abc0a96296