[Feature Request] Adding option to distable StandbyReplicas for OpenSearch Serverless

[statefb]

Describe the solution you'd like

Reduce option to disable StandbyReplicas for OpenSearch Serverless on Knowledge Base.

Why the solution needed

Standby replica is enabled by default, but in some cases e.g. PoC, users might want to reduce operational cost rather than availability.

Additional context

doc: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-opensearchserverless-collection.html

Implementation feasibility

Are you willing to discuss the solution with us, decide on the approach, and assist with the implementation?

• [x] Yes
• [ ] No