feat: event source mapping metrics support

[moritzzimmer]

This PR adds support for event source mapping metrics, see aws docs for details

[Copilot]

Pull Request Overview

This PR adds support for AWS Lambda event source mapping metrics configuration, allowing users to specify which metrics to collect for their event source mappings as documented in the AWS Lambda monitoring guide.

• Adds metrics_config dynamic block to the event source mapping resource
• Updates example configurations to demonstrate metrics_config usage with EventCount metric
• Reorganizes scaling_config placement in the SQS example for better readability

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
event_source_mappings.tf	Adds dynamic metrics_config block to aws_lambda_event_source_mapping resource
examples/with-event-source-mappings/sqs/main.tf	Demonstrates metrics_config usage and reorganizes scaling_config placement
examples/with-event-source-mappings/kinesis/main.tf	Adds metrics_config example with EventCount metric
examples/with-event-source-mappings/dynamodb-with-alias/main.tf	Adds metrics_config example and removes empty line

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