[feature request] changelog_url as output value

[Yago-Ferrer]

One of the output values is changelog and contains the following:

changelog=### [2.0](https://github.com/repo/compare/1.0...2.0) (2.0)

I have to write a custom commit message that contains the URL, but not the rest of the text. It would be nice if there's a changelog_url so that I don't have to write a regular expression against the text message provided in the changelog input value, or "construct" the URL myself.