Improve autoinstall schema for third-party drivers

The autoinstall data for the drivers was only constituted of a boolean,
e.g.:

  drivers: true

or

  drivers: false

It was not immediately clear that the boolean value meant (install/don't
install the drivers).

We now store the boolean in the "install" sub-element instead, e.g.:

  drivers:
    - install: true

  drivers:
    - install: false

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

autoinstall-schema.json

@@ -396,7 +396,12 @@
             }
         },
         "drivers": {
-            "type": "boolean"
+            "type": "object",
+            "properties": {
+                "install": {
+                    "type": "boolean"
+                }
+            }
         },
         "timezone": {
             "type": "string"

subiquity/server/controllers/drivers.py

@@ -33,17 +33,25 @@ class DriversController(SubiquityController):
 
     autoinstall_key = model_name = "drivers"
     autoinstall_schema = {
-        'type': 'boolean',
+        'type': 'object',
+        'properties': {
+            'install': {
+                'type': 'boolean',
+            },
+        },
     }
-    autoinstall_default = False
+    autoinstall_default = {"install": False}
 
     has_drivers = None
 
     def make_autoinstall(self):
-        return self.model.do_install
+        return {
+            "install": self.model.do_install,
+        }
 
     def load_autoinstall_data(self, data):
-        self.model.do_install = data
+        if data is not None and "install" in data:
+            self.model.do_install = data["install"]
 
     def start(self):
         self._wait_apt = asyncio.Event()