Add danger check for duplicate yarn dependencies
This danger check utilises `yarn-deduplicate` in order to show duplicate dependencies in the yarn.lock dependency tree. Often when introducing new dependencies or updating existing ones, yarn does not seem to build the most optimal dependency tree. In order to prevent those unnecessary dependency updates we are nudging developers and maintainers to resolve these issues in MRs. Automating this with danger especially helps, as yarn.lock files are not that easy to review.
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