Bump the minor version of the newest chunk on change allowMigrations and reshardingFields

Currently, when changing the 'allowMigrations' or 'reshardingFIelds' field on config.collections, we are bumping the major version of a random chunk (or one random chunk per shard in resharding_coordinator). This can be optimized by bumping only the minor version of the newest chunk. This achieves the same guarantees of ending up with a new collection version, but it avoid the drawback of invalidating the versioning info of a shard.