Include source code as asset in releases to avoid issues with GitHub compression algorithm changes

[kjlubick]

The rules_sass docs say to create an http_archive using a GitHub source archive URL like https://github.com/bazelbuild/rules_sass/archive/1.26.3.zip.

However, as was observed in a large outage on Jan 31, 2023, the compression algorithm used by GitHub can change, breaking sha256 validation.

The recommendation seems to be to include the source zip/tar.gz files in the release itself as an asset (like protobufs does). GitHub promises not to change those bytes since they are user-provided.

I notice there hasn't been an official GitHub release of rules_sass in a while. Doing so more regularly is a prerequisite to addressing this issue.

Then, the docs should show a URL like:
https://github.com/bazelbuild/buildtools/releases/download/1.26.3/source-1.26.3.tar.gz
depending on what file name for the source code asset is.