[Website]: Qualify Docker prune statement in troubleshooting documentation

### Before you submit

- [x] This issue is about a documentation page, flow, or piece of content.

### Type of issue

Missing information

### What documentation page or section is affected

https://www.elastic.co/docs/troubleshoot/deployments/cloud-enterprise/troubleshooting-container-engines

### What happened?

The current statement _"we advise against running any variation of Docker’s prune to avoid accidental data loss"_ is overly broad and lacks context.

We should clarify that this guidance applies specifically to active troubleshooting scenarios where system state may be unknown. If pruning is of concern, we should call out which subcommands as their risk differs greatly.
Consider noting that targeted cleanup of images with `image prune` may be appropriate as part of controlled maintenance, outside of troubleshooting workflows.

### Additional info

_No response_