[8.0](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: 2021-11-24T16:04:06.753+0000

• Duration: 74 min 56 sec

• Commit: 8555427

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Test	Results
Failed	0
Passed	2661
Skipped	240
Total	2901

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