Chatops should discourage feature flag changes with large percentage rollout changes

Issue originated from https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16261

In Chatops, implement a warning message if a new feature flag is enabled in a large percentage rollout step.

Probably involves adding an additional check here.

Questions that need to be addressed (probably during code review):

• should we skip this check for staging?
• where should the threshold be set?