Communication plan for error budgets for stage groups

We should make sure we sufficiently spread the word around the error budget when they have been added. I don't think we need to wait until completion of &437. As soon as the number is visible on the dashboard and the documentation from gitlab-org/gitlab!57853 (merged) and gitlab-com/www-gitlab-com!77903 (merged) has been merged.

The developer documentation explaining the calculation links to the ongoing work, so folks know to take the number with a grain of salt at first.

We should link to the documentation with a message in the following channels

• Engineering week in review
• #eng-managers