ci: generate preview deployments for each pull_requests

[moreal]

Context

Right now, we're struggling to make sure our deployments with changes are working well. It varies from network to network, and from PollerType to PollerType, so it would be nice to be able to actually run it and get a result, even if it's a manual human judgment.

This issue suggests a preview deployment per pull_request to open MongoDB, but other methods are fine too.