optimize: add ASF licence headers

add ASF header in there files:

./pkg/datasource/sql/undo/parser/branch_undo_log.pb.go
./pkg/discovery/mock/mock_etcd_client.go

Open pkg/datasource/sql/undo/parser/branch_undo_log.pb.go and pkg/discovery/mock/mock_etcd_client.go first. Compare their file headers with the repository's ASF header convention, add the required header to both files, and verify that each named file contains it.

Written by the indexing model from the issue text.