Source Package Generation in CI Pipeline

[nickclark2016]

What does this PR do?

Adds a job to generate source packages. This job depends on the Linux, Windows, and MacOSX jobs completing successfully, as these should be a prerequisite to building source packages (why build useless source packages?).

This also helps to automate a step of the Premake release process, where we'd be doing this manually.

How does this PR change Premake's behavior?

N/A

Anything else we should know?

N/A

Did you check all the boxes?

• [x] Focus on a single fix or feature; remove any unrelated formatting or code changes
• [x] Add unit tests showing fix or feature works; all tests pass
• [x] Mention any related issues (put closes #XXXX in comment to auto-close issue when PR is merged)
• [x] Follow our coding conventions
• [x] Minimize the number of commits
• [x] Align documentation to your changes

You can now support Premake on our OpenCollective. Your contributions help us spend more time responding to requests like these!

[nickclark2016]

FYI: The issue in the build pipeline is because it pulls the premake sources from GitHub and tries to run off those. Since my code is not in the repo, it can't actually run it. Quite a catch-22.