Update metadata on DORA pages

What does this MR do and why?

As per gitlab-com/www-gitlab-com!91295 (comment 694304702), DORA has transitioned from ~"group::release" to groupoptimize.

This MR updates the metadata for DORA pages to:

stage: Manage
group: Optimize

Pages in scope:

• https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/api/dora4_project_analytics.md
• https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/api/dora/metrics.md

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