feat: allow to overwrite event id strategy

[Grzesie2k]

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

We can change the way EventBus retrieves event IDs by extending this class and overriding EventBus.getEventId. However, if we do that, registered handlers will not be found because defaultReflectEventId is used in EventBus.registerHandler.

Issue Number: N/A

What is the new behavior?

We can change the way EventBus retrieves event IDs by assigning a different strategy to EventBus.eventIdProvider (similarly to EventBus.publisher), and there are no issues with registering handlers.

Does this PR introduce a breaking change?

• Yes, but only in the case of an implementation that extended the eventBus class.
• No

If you're extending the EventBus class in your code and relying on EventBus.getEventId, you should refactor the code to use this.eventIdProvider.getEventId instead.

Other information