Adding Meta fields to messages in mapping proto to support metadata entries.
Adding Meta fields to messages in mapping proto to support metadata entries.

PiperOrigin-RevId: 338704712
Change-Id: I3addc0e083807f35798733a3ca2bfb54a26a152c

GoogleCloudPlatform/healthcare-data-harmonization,GoogleCloudPlatform/healthcare-data-harmonization,GoogleCloudPlatform/healthcare-data-harmonization,GoogleCloudPlatform/healthcare-data-harmonization,GoogleCloudPlatform/healthcare-data-harmonization,GoogleCloudPlatform/healthcare-data-harmonization