feature request: subscribe cloudwatch alarms to a sns topic(configurabable)

**Required Info:**
- AWS ParallelCluster version [e.g. 3.1.1]:3.8+
- Full cluster configuration without any credentials or personal data.
- Cluster name:
- Output of `pcluster describe-cluster` command.
- [Optional] Arn of the cluster CloudFormation main stack:

**Bug description and how to reproduce:**
Currently, cloud watch metric alarms are created for each cluster, but no notification actions are assigned.

This request is to make it to configurable to use a pre-created SNS topic for such alarms.

Start with the cluster configuration and alarm creation path, using the pcluster describe-cluster command to understand the current cluster outputs. Trace how CloudWatch metric alarms are created and determine where a pre-created SNS topic could be configured. Done means cluster alarms use the configured topic for notification actions.

Written by the indexing model from the issue text.