Workhorse not allowing multiple files for upload

Summary

We support uploading designs up to 10 times (#13407 (closed)) but we are only allowing 1 file upload at a time at workhorse level: https://gitlab.com/gitlab-org/gitlab/-/blob/9aaf54dc9c009e4a75d86898fcde1d09561a42b1/workhorse/internal/upload/rewrite.go#L120-122.

Steps to reproduce

1. Create an issue.
2. Upload 2 designs at a time.

You'll see an error that designs failed to upload.

Example Project

Tried it here patrickbajao/verification#5.

What is the current bug behavior?

It does not allow multiple designs to be upload in a single request. But still allows uploading one at a time.

What is the expected correct behavior?

Multiple designs should be allowed to be uploaded.

Possible fixes

Increase the limit at the workhorse level to 10 to accommodate multiple file uploads without eating too much resources.