[awsfirehose] Add routing rules for metrics ingested from Firehose

[kaiyan-sheng]

Proposed commit message

This PR is to add routing_rules.yml for metrics ingested from Firehose. Without this integration or user specific set the parameter in Firehose, metrics coming into Elasticsearch by default goes to metrics-aws.cloudwatch-default. Idea to reroute is by checking the value of aws.cloudwatch.namespace field in each document to decide which data stream to route the document to. For example if aws.cloudwatch.namespace equals to AWS/EC2, then this document should go to metrics-aws.ec2_metrics-default.

For s3 daily storage and s3 request, we check for the actual metric name. If metric name is either BucketSizeBytes or NumberOfObjects, this document goes to aws.s3_daily_storage. If it's other metric name but still with AWS/S3 namespace, documents go to aws.s3_request.

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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