Should normalize update minor_version?

Currently if I run a v 4.0 notebook through `nbformat.validator.normalize`, it will add cell ids, but it will leave the minor version as 0. Shouldn't it be updated to 5 to highlight that it now includes some fields that was added in that version of the schema? Since the previous versions have the schema with `additionalProperties: false`, the new notebook will be invalid against the 4.0 schema.

Start at the nbformat.validator.normalize entry point and trace how it handles notebook versions, cell IDs, and schema fields. Confirm whether normalization should update minor_version from 4.0 when it adds fields introduced by version 5, then verify the resulting notebook against the relevant schema.

Written by the indexing model from the issue text.