Added a new example upload script for parallel upload.

examples/external_project_parallel_upload/example-1.tar.gz

examples/external_project_parallel_upload/example-2.tar.gz

examples/external_project_parallel_upload/example-3.tar.gz

examples/external_project_parallel_upload/externalproject.py

examples/external_project_parallel_upload/upload.py

...ples/external_project_upload/external_project_example.zip

examples/external_project_upload/upload.py

nomad/app/api/upload.py