Adds draft GH release and Hackage release CI workflows

[DavidMazarro]

This PR adds a draft release workflow to the CI pipeline, mostly brought over from Hapistrano, but removing the caching and Docker stuff. It also adds the Hackage release upload workflow (also based in Hapistrano's) to automate the process of bundling the library for Hackage, with the Haddock documentation, etc. (see our custom action for details).