Add release workflow for litani

[ronakfof]

Tests
Example Release - [workflow]
Deb package - [workflow]
Example PR to tap - [workflow]

Description of changes:

This workflow gets triggered when a tag is pushed of format litani-*.
Bot creates a release for that tag with a boilerplate description.
If a release is created successfully, it also creates a debian package for Litani on ubuntu-20.04, tests it and uploads it as an additional asset to the release and also create a PR to aws/tap with updated version, tag and commit.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[karkhaz]

Looking forward to this. My main question is whether we can integrate the changelog into the release notes.

Maybe the right thing to do here is: instead of this workflow triggering on litani-* tag, it would trigger on any commit that gets pushed with an updated changelog. In that case, it would take the release notes from the changelog, and the workflow itself would create the release tag.

So from a user perspective, when we want to create a new release, we add to the CHANGELOG and push that change to the develop branch, and this workflow would merge the release branch into that commit and tag it as the next release.

That might be more complicated though because the workflow itself would have to figure out the release number... But I'm quite keen for the release notes to end up in the tag message.

[karkhaz]

This is awesome :)