Support running bin locally with no credentials

[burke]

I have a CI failure due to smart_todo here: https://buildkite.com/shopify/dev/builds/13584#8c3ee7ca-e462-4f27-a38a-b6d951a562af

In order to debug this, the first thing I tried is to run bin/smart_todo locally, but it won't let me.

It would be really useful if it supported running locally without credentials, but just printing the triggered conditions.

[Edouard-chin]

Ack, thanks for the report.

I'll add a dry run options which will be the default if no credentials are given