[CMAKE] add generated protobuf headers to the opentelemetry_proto target#3400

lalitb merged 5 commits intoopen-telemetry:mainopen-telemetry/opentelemetry-cpp:mainfrom

dbarker:fix_opentelemetry_proto_target_includesdbarker/opentelemetry-cpp:fix_opentelemetry_proto_target_includesCopy head branch name to clipboard