Update grpc error codes in Kingdom Internal Services about cross-media-measurement HOT 1 CLOSED

Parent not found -> FAILED_PRECONDITION

More clearly, the internal services shouldn't make a distinction about what's a "parent". This is something the public services do because they have a defined resource hierarchy where a resource's name may include a parent.

The distinction that internal services need to make is based upon whether the problem is that the entity being acted upon couldn't be found, vs. whether some other entity couldn't be found.

There's arguments both ways re: whether to use FAILED_PRECONDITION or NOT_FOUND from internal services when a "parent" entity isn't found. The main point is that internal services need to provide their callers with enough information to accurately return their own correct Status.

some resource other than parent or self not found -> INVALID_ARGUMENT

I think this should be FAILED_PRECONDITION. As per Status codes and their use in gRPC, INVALID_ARGUMENT is for when the arguments are incorrect regardless of the state of the system (e.g. some field is malformed or missing). In this case, the arguments could be correct if the entity with the given ID already existed. The fact that the system happens to always assign random IDs is irrelevant.

from cross-media-measurement.