0.12.8

Backporting fixes:

• Remove .to_timestamp() to fix interval plotting #2800 by @abdulfatir
• Fix pd.Period serialization #2827 by @abdulfatir
• Remove second call to create_lightning_module on torch estimator #2834 by @pablovicente
• Fix torch DeepAREstimator in case context_length=1 #2841 by @lostella
• Ignore hidden files in FileDataset by default. #2847 by @jaheba