[11.x] Add addEventDiscoveryPaths to EventServiceProvider

[ya-cha]

This pull request introduces the capability to append discovery paths to the EventServiceProvider, rather than overwriting the entire array.

In our application, we manage a domain structure where each domain has its own event listeners. Shared Listeners are still in the original location.

In our DomainServiceProvider we iterate through those domains add register views, Livewire components etc. This enhancement allows us to add discovery paths in the DomainServiceProvider without overwriting the existing paths. This way, each domain can register its listeners independently.

Since I did not find tests for the method setEventDiscoveryPaths, I did not add any for the new method.