Add pre* change types by default

[ecraig12345]

There are additional change types prepatch, preminor, premajor which beachball doesn't fully support today. Making these available by default outside of a major version bump would be perceived as a breaking change, but we should consider adding them in the next major version.

(As of #944, beachball will allow these change types if specified with --type on the command line, by editing the change files, or with a custom change type prompt. But they won't show up in the change type prompt by default.)

Alternatively, we could add another option like includeAllPrereleaseTypes which makes the extra prerelease types show up by default when prerelease. Or also fix one of the issues referenced by #21 and add an option like showPrereleaseTypes: ChangeType[] which makes those prerelease versions show up in the prompt even when the current version isn't a prerelease, and ask for the prerelease prefix if not specified (maybe have a default option for that too?).