Need to store zone image source for inventory zones

[plotnick]

Right now, blueprint zone descriptions store an image source in the database, but inventory zone descriptions do not. This prevents us from matching image sources specified in a blueprint with the actual zones collected during inventory. We should copy the blueprint's image source fields and handling over to the inventory.

[davepacheco]

From discussion in today's update watercooler, we believe that sled agent is already reporting this information correctly, and the initial in-memory inventory collection probably has it, but it's being dropped when Nexus stores the inventory collection into the database and so it's missing when it gets read back out of the database. What's probably missing then is:

• nexus-db-model type needs to include this information
• database schema needs to include this information (can maybe rename and re-use the types used for the blueprint version of this information)
• DataStore::inventory_insert_collection needs to save it
• the DataStore function that reads the collection from the database needs to read it
• omdb command for showing inventory should show this field
• ideally: reconfigurator-cli command for showing inventory should show this field