[AWS] Fix billing dashboard metric name

[kaiyan-sheng]

What does this PR do?

This PR is to fix the billing dashboard that's broken by PR. Field aws.billing.metrics.EstimatedCharges.max is renamed to aws.billing.EstimatedCharges but not in the dashboard.

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.

Related issues

• Closes [AWS] Fix billing dashboard metric name #2946 (comment)

[elasticmachine]

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• Start Time: 2022-03-31T16:05:31.931+0000

• Duration: 31 min 30 sec

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Test	Results
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Passed	327
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Total	327

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