How do I find out what IAM user created certain metrics and alarms?
I tried CLI commands: describe-alarms and list-metrics and they don't seem to provide this information nor when looking at the configuration for the alarms and metrics in the AWS console.
While users call APIs to create resources in AWS, those resources are associated with the AWS Account rather than a user. As long as a user has permission to create resources in the account, the resources will be created/viewed/deleted.
However, you can use AWS CloudTrail to retrieve information about the API calls themselves:
AWS CloudTrail is an AWS service that helps you enable governance, compliance, and operational and risk auditing of your AWS account. Actions taken by a user, role, or an AWS service are recorded as events in CloudTrail. Events include actions taken in the AWS Management Console, AWS Command Line Interface, and AWS SDKs and APIs.