feat(publication): add shasum files to release

Hello 👋

Currently, only binaries are published, and sha digests are part of the release note.
For automation purpose, it would be good to have those digests directly in the release, so we can download them using the `github` API, like for the original binary.

With it, we won't rely on flaky html parsing to achieve digest extraction.

PS: Of course, this is useless if https://github.com/aptible/supercronic/issues/139 is implemented.

Thank you

No file or test is named. Locate the release configuration or workflow that publishes binaries, then trace how the current digests are generated and included in release notes. Done means each published binary also has a downloadable checksum file accessible through the GitHub release API.

Written by the indexing model from the issue text.