Appliance fields that describe the appliance (vendor information, default
credentials, installation instructions...) were dropped when installing a
template. Keep them in a new appliance_metadata JSON column on the
templates table, filled by the appliance-to-template conversion for both
registry v1-6 and v8 (version level values override the appliance level
ones). The nested schema allows extra fields so future registry fields
persist without a migration.
- install: resolve the image directory from the version's settings type and
skip image handling for docker appliances; guard appliance.images
- appliance schema: validate template_properties against template_type,
align cpu_throttling with the qemu template, add kvm and version idlepc
- conversion: map IOU image to path, kvm disable to accel=tcg, inherit only
same-type default settings, symbol fallback from the effective category,
template_properties cannot override structural fields
- allow clearing netmiko_device_type with an empty string
- download the template symbol regardless of the level it is defined at and
give qemu guests a default symbol
