bug: Multiple data loaders found shown happens when handling requests

[kzwang]

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Expected behavior

When multiple data loaders are using @DgsDataLoader with the same name, it should validate that and fail early.

Actual behavior

App starts up successfully, but failed to handle requests with error "Multiple data loaders found"

Steps to reproduce

Note: A test case would be highly appreciated, but we understand that's not always possible

[mrvaruntandon]

@kzwang in which version you are seeing this issue?