Add generic interface for accessing device features (#741)

This adds a generic interface for all device classes to introspect available device features,
that is necessary to make it easier to support a wide variety of supported devices with different set of features.
This will allow constructing generic interfaces (e.g., in homeassistant) that fetch and change these features without hard-coding the API calls.

`Device.features()` now returns a mapping of `<identifier, Feature>` where the `Feature` contains all necessary information (like the name, the icon, a way to get and change the setting) to present and change the defined feature through its interface.

kasa/iot/modules/cloud.py

@@ -4,6 +4,7 @@ try:
 except ImportError:
     from pydantic import BaseModel
 
+from ...feature import Feature, FeatureType
 from .module import IotModule
 
 
@@ -25,6 +26,24 @@ class CloudInfo(BaseModel):
 class Cloud(IotModule):
     """Module implementing support for cloud services."""
 
+    def __init__(self, device, module):
+        super().__init__(device, module)
+        self._add_feature(
+            Feature(
+                device=device,
+                container=self,
+                name="Cloud connection",
+                icon="mdi:cloud",
+                attribute_getter="is_connected",
+                type=FeatureType.BinarySensor,
+            )
+        )
+
+    @property
+    def is_connected(self) -> bool:
+        """Return true if device is connected to the cloud."""
+        return self.info.binded
+
     def query(self):
         """Request cloud connectivity info."""
         return self.query_for_command("get_info")