[7.16](backport #29106) Fix rds metadata in cloudwatch metricset

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This is an automatic backport of pull request #29106 done by Mergify.

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• Start Time: 2021-11-24T17:47:52.067+0000

• Duration: 80 min 7 sec

• Commit: 204a813

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Test	Results
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Passed	2666
Skipped	248
Total	2914

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