Add Validator setter in EndpointRegistrar

[mt-ocado]

📢 Type of change

• Bugfix
• New feature
• Enhancement
• Refactoring

📜 Description

Add Validator setter to EndpointRegistrar that is propagated to the HandlerMethodArgumentResolver instances configured in AbstractListenerAnnotationBeanPostProcessor.

💡 Motivation and Context

Discussed in #854.

Currently, there is no easy way to set up validation for payload in the listener methods. The PayloadMethodArgumentResolver and BatchPayloadMethodArgumentResolver have set null for the validator field which means they never will validate the payload. This change will propagate the Validator set in EndpointRegistrar.

💚 How did you test it?

• Unit test
• Manual test

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated reference documentation to reflect the change
• All tests passing
• No breaking changes

🔮 Next steps

[tomazfernandes]

Hi @maksym-telepchuk-ocado, looks great, thanks for the PR!

[marcussatelis]

Should have used jakarta.validation.Validator not?