[AWS][cloudwatch_metrics] Use object metric type for the cloudwatch metrics

[tetianakravchenko]

What does this PR do?

In this previous PR - was mentioned that the expected field definition is:

type: object
object_type: double
object_type_mapping_type: "*"

As was mentioned in this comment defining type: double is not equal to the above, due to some differences in the generated dynamic_template. So was decided to switch back to the previous format

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• [ ]

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• Start Time: 2023-08-09T12:51:54.661+0000

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Package aws - 1.51.1 containing this change is available at https://epr.elastic.co/search?package=aws