feat(release): Delegate version bumping to Craft

[iker-barriocanal]

At the moment, buildVersionCode and versionName have to be updated manually before doing a release. This PR adds a version bumping script, run by Craft on prepare.

• buildVersionCode will be incremented by 1.
• versionName will be the new version to prepare by Craft. For example, craft prepare 6.0.0 will set versionName=6.0.0, and craft prepare 6.1.0-alpha.1 will set versionName=6.1.0-alpha.1.

Note Changelog Policies. Current policy is simple, so there must be an entry in the changelog with a matching version name for the new release passed to Craft; if not, the command will fail.

#skip-changelog

[marandaneto]

@iker-barriocanal looks like we could change https://github.com/getsentry/craft#changelog-policies to auto then, as we currently maintain the Unreleased label