Pytorch-lightning: Support OmegaConf dicts in hparams

[Darktex]

🚀 Feature

Lightning hparams were recently changed to support only dicts and ArgParse namespaces. This diff (re)introduces compatibility with OmegaConf DictConfig, which is the type of config that Hydra uses.

Motivation

Using Hydra + Lightning

[calclavia]

Running into the same issue when trying to use things like auto_lr_find
pytorch_lightning.utilities.exceptions.MisconfigurationException: When auto_lr_find is set to True, expects that hparams either has fieldlrorlearning_ratethat can overridden

[stale[bot]]

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