[Design Management] Allow designs to be renamed

About

As a user, I would like to be able to rename a design.

backend Technical proposal

We would separate the name of a design from the extension, to make it easier for renaming designs. #208384 (comment 295779354).

names should not be allowed to have . in them, but could have spaces.

• See the blocking issues #208384 (closed)
• Migrations to separate the file extension from the file name
• Probably a data migration to backfill records
• A new designManagementRenameDesign mutation