Consolidate DORA docs

What does this MR do and why?

Originally, DORA metrics were introduced as part of CI/CD analytics and only later we added the APIs the tiles to VSA and Insights. As a result, DORA capabilities are now spread across multiple platform pages. Following the new category for DORA, we need to consolidate our DORA docs in one page.

This related to Add new DORA Metrics category (gitlab-com/www-gitlab-com!111590 - merged)

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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.

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

doc/user/analytics/ci_cd_analytics.md

@@ -100,7 +100,7 @@ To view the time to restore service chart:
 
 The change failure rate chart shows information about the percentage of deployments that cause an incident in a production environment. This chart is available for groups and projects.
 
-Change failure rate is one of the four [DORA metrics](index.md#devops-research-and-assessment-dora-key-metrics) that DevOps teams use for measuring excellence in software delivery.
+Change failure rate is one of the four [DORA metrics](../../ee/user/analytics/ci_cd_analytics.md#devops-research-and-assessment-dora-key-metrics) that DevOps teams use for measuring excellence in software delivery.
 
 To view the change failure rate chart: