Fix yamllint violations in metrics yamls

What does this MR do and why?

While reviewing a citemplates MR, I noticed that a key was duplicated in one of the metrics yaml files. I did a quick scan and found several violations and thought it would be good to clean them up, especially the duplicates keys.

• Related to Add milestone <13.9 to metrics with no milestone (!69400 - merged)
• Related to Import remaining metrics definitions (!55846 - merged)
• Related to Make product_stage required, allow null values (!69897 - merged)
• Related to Added unapprove quick-action (!69225 - merged)

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