Allow batch uploads in bugit.submit

submit multiple report tar files to the same project

Start at the bugit.submit entry point and inspect how it currently handles one report tar file and selects the target project. Trace the existing single-file submission path before determining where multiple files can be accepted for the same project. Done means one invocation submits multiple report tar files while preserving the existing single-file behavior.

Written by the indexing model from the issue text.