Enhancement for staff to have ability to edit a unit notes.

Staff request the ability to edit unit notes. Currently a unit note can be created, cancelled or a notice of redemption can be issued, but it is not possible to edit a unit note. Staff needs to edit/update unit notes sometimes and it would be useful to have the option.
Currently they need to cancel and create a new one.

Need to check with staff:
- How often editing a unit note is used, eg: on the green screen when or in which cases is it used.

No files or tests are named. First confirm with staff how often unit notes need editing and which green-screen cases require it, then trace the existing create, cancel, and notice-of-redemption workflows. Done means the supported edit cases and implementation scope are agreed.

Written by the indexing model from the issue text.