Streamline Artifact Upload

Right now the artifact upload is kind of simple. A container is created and a set of files are added to it.

This has the following downsides:

• If the build artifact is already an archive like a tar archive or even an rpm or deb package it will be packaged again into a zip file. For outside testing / using the container archive has to be unpacked and then the inner archive has to be unpacked as well. Install packages have to be unzipped before they can be used.
• If many small files are added to the artifact (e.g. to avoid two nested archives) an http request is done for each file. Even though some requests are parallelized the extra time and compute power wasted is significant, depending on the file size.

Possible solutions:

1. Allow a single artifact upload mode, that is not wrapped into an extra archive. It would be wise to limit the file types that are allowed in this mode to avoid abuse.
2. Upload multiple files in one http request to the artifact container. Possibly using multi part mime encoding or a simple container format like tar. The files may be reasonably chunked to allow outputting progress details.

Both options would save energy for Microsoft / Github, reduce the cycle time for GHA and time for the users.

The issue names no files, tests, or entry points. Start by locating the artifact upload implementation in actions/toolkit and clarify whether the intended direction is unwrapped single-artifact uploads, batched multi-file requests, or both; done requires an agreed design that addresses redundant packaging and per-file request overhead.