Support creating a source package without using the artifacts API

[daviddavis]

Is your feature request related to a problem? Please describe.
Today in order to create a source package in pulp_deb, you first have to upload the source tarballs as artifacts. This is unlike other content types which allow you to call a single endpoint to create the package, etc.

Describe the solution you'd like
Ideally, we'd like a way to create source packages without calling the artifact api. It sounds like Pulp is moving away from supporting the artifact API with possibly removing the API in Pulp 4.

There are some different solutions we discussed like using a multipart request to submit multiple files to POST /pulp/api/v3/content/deb/source_packages/. Or possibly using the upload API (/pulp/api/v3/uploads/) to upload the necessary artifacts.

Additional context
Info about source packages: https://wiki.debian.org/Packaging/SourcePackage