Share ChatOps feature flag results with DRI's team

What does this MR do and why?

This MR suggests to cross-post results of #production feature flag rollouts in the Slack channel of the DRI's team. Same channel indicated in the rollout issue.

The goal of this change is to increase visibility across the team members and help correlate any occurring production incidents.

Related to gitlab-com/www-gitlab-com!92731 (comment 717004698)

Screenshots or screen recordings

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How to set up and validate locally

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MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.