Validator client subscription to slashing SSE events

### Problem description

With the implementation of #6209 to detect slashable events, it still requires either useful infrastructure/3rd party software to take advantage of this feature. An idea is to further extend this into our validator client to benefit from this was brought up by @g11tech.

### Solution description

By implementing a feature for alerting VCs of the signed messages, or having the connected validator to subscribe to these events, we can have the validator client itself be aware that one of their local pubkeys is being slashed. Then, we can implement some action (e.g. shutting down the service) to prevent further slashings.

### Additional context

_No response_