effects/github-releases: needed functionality

[Kranzes]

• Be able to "update" a previous release with the same tag as the current one. This is useful when you want to keep the same tag but update the uploaded assets. Here's an attempt on how It should work: Kranzes@be649c9
• Make hercules-ci.github-releases a submodule so you can deploy multiple releases from the same flake
• Make an option to set the release title, context: gh release has the --title flag
• Expose a read-only option that has the value of all the files in the file spec, (List of attrs with label/path)

[Kranzes]

cc. @Mr-Andersen