Docs: Feedback for Configure Shadowing on Cloud

[treevon]

Issue description

Lack of detail in how to specify multiple topics or consumer groups in shadowing configuration. it should be explicit that only one pattern should be present in a filter.

Updates to existing documentation

Configure Shadowing Page source

Link to Redpanda Slack conversation

https://redpandadata.slack.com/archives/C0191NM4WU9/p1773870768669519