Unintuitive automatic pause behavior for blue green strategy

[jessesuen]

The current automatic pause behavior for the blue/green strategy is inconsistent, and hard to explain. Some examples:

• it does not pause during the initial rollout
• it does not pause if the preview service is unspecified, but will pause if it is.
• it does not pause during a fast rollback

These rules are not obvious or documented. I think we need to rework the behavior so that it is more easily predictable.

I also feel the default behavior should be switched to automatically perform a cutover instead of the current behavior of automatically pausing if there is a preview service. This would make it consistent behavior with rolling update, recreate, canary, where the default behavior is to perform the promotion automatically. Just because I don't specify a preview service, doesn't necessarily mean I don't want it to pause, and vice versa.

[jessesuen]

Another problem is that there is no a way to automatically pause a blue green rollout before cutover, unless I specify a preview service.

[jessesuen]

Fixed with spec.autoPromotionEnabled field