Ability to send metrics to existing domain

[prashanttct07]

Current stack provisions a new domain for storing the KPI and Metrics, as part of this feature I would like a configurable option where customer can provide the details of an existing Amazon OpenSearch Service Domain, and stack creates the necessary components only for extracting the metrics. And then those components should send the metrics to existing Domain provided by the user.

This will also include skipping an EC2 instance created for proxy, and bootstrap operations such as roles, alerts, templates should be created via lambda as one time operation. (Lambda is a suggestion, other operations could also be explored if needed)