Export CLI

[skipjack]

As noted in #98 and this comment, it would be great to have a CLI for exports so that we can...

• Remove the need for the manual step if you're always exporting all suites.
• Address the security issues involved with including the exported project in a git repository, similar to my comments about hidden template variables in Improve Hidden Template Variables #86 they're also unprotected plain text in the exported project. This means that if you have to push that directory rather than programmatically generating it fresh before each run then you're exposing the credentials in your git history (something that's not easy to walk back).

This could even be a separate repo / npm package allowing for something like...

puppetry export --environment=test [suites or * for all]

With that in place, users would no longer need to manually export and include their tests in git. They could simply have a GitHub Action (GitLab CI, Circle CI, Travis, etc) that runs the export cli and then jumps into the directory to install dependencies and run the tests. I know CI Tools might not be the only place these tests are run but most allow scheduling which means you can easily run tests in a cron-like fashion as well as a ci-like one.