Some existing or custom extra fields may be actually shorter than 2 letters (e.g. [cities](https://en.wikipedia.org/wiki/List_of_short_place_names)). This decreases the `min_length` of these fields to `1`.
*JIRA tickets*: TBD
*Merge deadline*: None
1. Set `city` to `required` in `lms.env.json` and restart LMS.
1. Register with one-letter city on `master` branch.
1. Register with one-letter city on this branch.
[ ] @giovannicimolin
[ ] edX reviewer[s] TBD