Prevent loadbalancer filter to wrap exception into RuntimeException

[ComputerDaddyGuy]

Current behavior

• In order to allow loadbalancer lifecycle processors to handle failed requests, the lb filter catches any Exception thrown from subsequent filters. After processing, the exception is rethrown but wrapped into a RuntimeException
• This wrap is (I suppose) originally due to usage of lambda, which does not allow to throw checked exceptions.

return (request, next) -> {
	// ...
	try {
		// Call subsequent filters
	}
	catch (Exception e) {
		supportedLifecycleProcessors.forEach(...); // Handle CompletionContext.Status.FAILED
		throw new RuntimeException(e); // <-- wrap and rethrow
	}
};

Issue

• Wrapping into a RuntimeException prevents error handlers to catch the original exception

var builder = RouterFunctions.route();

// Not working because of RuntimeException wrap
builder = builder.onError(MyCustomException.class::isInstance, (ex, request) -> ...);

// Custom exception is catched here
builder = builder.onError(_ -> true, (ex, request) -> ...);

Proposed solution in this PR

• The lb filter has been adapted to use an anonymous class instead of a lambda
• The original exception is rethrown as is, without any change or wrap
• A test has been added to ensure the lb filter does not wrap the original exception