[AWS] Fix rds field description aws.rds.cpu.total.pct

[kaiyan-sheng]

Proposed commit message

Based on the code where the RDS CPU metric is collected, this value is divided by 100: https://github.com/elastic/beats/blob/v8.10.2/x-pack/metricbeat/module/aws/cloudwatch/metadata/rds/rds.go#L40
Fixing the documentation to not say percentage in the field description.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @kaiyan-sheng? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

Pinging @elastic/obs-ds-hosted-services (Team:obs-ds-hosted-services)

[elasticmachine]

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• Start Time: 2024-04-09T03:34:37.374+0000

• Duration: 78 min 12 sec

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