Don't Require knope.toml for basic release workflow

[dbanty]

To make adoption even easier, it would be a good idea to allow someone to run basic workflows (notably knope release for starters) without any configured knope.toml. This will inspect the project the same way knope --generate does to determine the best guess for a release workflow, then run it.

It may be worth making some of the output more verbose so people can see what knope thinks is the right thing—particularly with knope release --dry-run.

Further, if a project does have a knope.toml but does not declare any of the built-in workflows—the built-in flows can still be called (a la cargo-make).