Handle OSS notices for envoy-mobile and diamond dependencies

[ryan-lane]

ios and android need to provide legal notices for OSS software that gets shipped to clients. The notices will need to be updated for envoy-mobile, and all of envoy-mobile's diamond dependencies.

All end-users of this software will have the same requirements, so an approach that easily handles this for Lyft and for downstream users would be ideal.

An approach that would likely work here, is to ensure the NOTICE file includes information for all dependencies (ideally diamond dependencies).

[mattklein123]

cc @rebello95 @buildbreaker to advise on how we are handling other SW and whether we can do anything generic here that will help all users of the library.