Update Prerequisites and System Requirements with Exporter Compatibility.

Under Prerequisites and System Requirements section of Couchbase Operator, we define the compatibility matrix of Fluent-bit and Operator Backup from our sidecar components.

https://docs.couchbase.com/operator/2.3-beta/prerequisite-and-setup.html

However, we seem to not define it for Prometheus Exporter for any releases of CND. We should change that for 2.3.0-GA to track exporter compatibility.

Opened a K8s ticket since the changes will be reflected in Operator builds.

CC: Simon Murray in case the decision was made not to put exporter section. In which case, Please feel free to close out this ticket.