[Feature Request] supply monitor_agent stats via RPC or update without_source to skip type monitor_agent

### Is your feature request related to a problem? Please describe.

A times we need to run fluentd without_source to halt input and aide in backend flushing.
When doing so - we do not have a method to pull the stats that are normally provided via monitor_agent.

### Describe the solution you'd like

supply monitor_agent stats via RPC or update without_source to skip type monitor_agent

### Describe alternatives you've considered

N/A

### Additional context

_No response_

Begin by examining the monitor_agent and without_source paths, then review the existing RPC behavior mentioned in the request. Determine which monitor_agent statistics must remain available when inputs are halted and define whether RPC exposure or skipping monitor_agent is the intended behavior; done requires an agreed design and coverage for that behavior.

Written by the indexing model from the issue text.