Add proto3 support for care_map

Switching to the protobuf format helps to make the care_map more
extensible. As we have such plans in the future, add the support to
parse the protobuf message in the update_verifier.

Bug: 77867897
Test: unit tests pass, update_verifier successfully verifies a care_map.pb
Change-Id: I9fe83cb4dd3cc8d6fd0260f2a47338fe142d3938