Add semanting release bot

[afontcu]

Other Testing Library members are using https://github.com/semantic-release/semantic-release to handle their releases.

It looks great not only because of the sensible version bumping, but also for all the automated tasks it handles (notifications, formalized commits,...).

Thoughts?

[dfcook]

Would be very happy to go with this, getting the release process into CI was one of the things on my todo list.

[afontcu]

Great! semantic-release relies on commit messages to infer new versions, so AFAIK that would mean implementing a tool such as commitizen.

Not sure what are the implementation steps, but I'll open a PR so that we can see what are the main changes.