Ui/Api : Allow updating "Read Instance settings from OVA" true/false

### The required feature described as a wish

As a User/Admin/Operator I would like to have the ability to change template property

Steps to reproduce the issue

1. Register the template with "Read Instance settings from OVA"

2. Try to edit the template , there is no option to disable the "Read Instance settings from OVA""

If there are no instances deployed from the Template, Admin/User should be allowed to change the Template setting “Read Instance settings from OVA”

Start by tracing the template edit UI and API handling for the “Read Instance settings from OVA” property, using the registration flow as the reference for its current behavior. Done means the setting can be changed in both UI and API when no instances use the template, while preserving the restriction when instances exist.

Written by the indexing model from the issue text.