Implement an upgrade procedure to populate range deletion task document with the key pattern.

This is a necessary step to simplify the shard key pattern retrieval starting from v8.1, as it will be guaranteed that no range deletion task document are written down without the key pattern field (hence, no refreshes will be needed).

It will not be necessary to delete the field on downgrade as keeping it doesn't harm: the parsing of range deletion documents is not strict and the field will simply be ignored.