0.10.3

Backporting fixes:

• Fix Prophet wrapper to work with Timestamp instead of Period (#2182 by @lostella)
• Fix dtype for "item_id" column in metrics dataframe (#2183 by @lostella)
• Fix recursive case for gluonts.mx.batchify.stack (#2184 by @lostella)
• Fix: ensure last cell of tutorials runs (#2186 by @lostella)
• Fix item_id values in ConstantValuePredictor (#2192 by @codingWhale13)