Always set ignored_safeties when emergency mode is enabled

[actgardner]

We're looking for ways to work Binary Authorization breakglass into the existing deploy workflow. One proposal was to trigger breakglass on an emergency deploy (see https://github.com/Shopify/production-registry/pull/245)

A deploy blocked by Binary Authorization may have a green CI status. For this reason, we need to either:

• always set ignored_safeties when the Emergency Deploy mode is enabled, even if CI is passing
• create a new database field and environment variable which is similar to ignored_safeties, but which is always set when Emergency Deploy mode is enabled

This PR takes the first approach and changes the behaviour of the existing field.

[DazWorrall]

Hmm, I worry this would create false positives in github-certification, @casperisfine wdyt?

[casperisfine]

I worry this would create false positives in github-certification

Yeah, I had the same worry.

I think overall this would be better handled with a boolean deploy variable. I also wonder if that makes sense as an open source feature.

[actgardner]

I think overall this would be better handled with a boolean deploy variable. I also wonder if that makes sense as an open source feature.

Like this? https://github.com/Shopify/shipit/pull/1037

[casperisfine]

Yes, exactly what I had in mind.