Feature flag rollout template to include release post updates

What does this MR do and why?

Related to #338163 (closed)

This MR adds a note to the feature flag rollout issue template to ensure that any breaking changes are called out via the release post process prior to being rolled out. Why? Because if you enable a breaking change without first alerting customers and account managers it can result in production incidents which are a huge disruption for everyone.

This MR follows a corrective action in which we add restricting permissions for the dependency proxy and did not announce the change and it resulted in a production incident and customer fallout.

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