Upload assets prior to creating a release using the generic package registry

Upload assets prior to creating a release using the generic package registry. This issue is a follow-up from #54 (closed)

Reference MR !59 (closed)

1. Add API call to generic packages to upload files to the release-cli.
2. Add flags --upload-dir and --package-name. Only support root level items and ignore subdirectories.

Related to &4209 (closed)