Rollout [Feature flag] `product_intelligence_metrics_names_suggestions` [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Rolls out product_intelligence_metrics_names_suggestions feature flag

This feature flag change only impacts custom rails generator used to automate metrics YAML generation https://docs.gitlab.com/ee/development/usage_ping/metrics_dictionary.html#create-a-new-metric-definition

This feature flag does not have any effect on production environments, and was only used on local development envs

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Does this MR meet the acceptance criteria?

Conformity

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  • I have included a changelog entry.
  • I have not included a changelog entry because it is a tooling change.
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• [-] Database guides
• [-] Separation of EE specific content

Related to #323460 (closed)