Update the feature flag rollout template to use multi-env command

What does this MR do and why?

This MR updates the feature flag rollout template to use multi-env command.

Closes gitlab-com/chatops#120 (closed)

Screenshots or screen recordings

Confirmed working in https://gitlab.slack.com/archives/CB2S7NNDP/p1655102284175949.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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