Show current license usage when updating Kentik license of a router

We now showcase the amount of devices already using this license, and the max amount of devices that can be assigned to it

gso/services/kentik_client.py

@@ -109,7 +109,42 @@ class KentikClient:
         return {}
 
     def get_plans(self) -> list[dict[str, Any]]:
-        """Get all Kentik plans available."""
+        """Get all Kentik plans available.
+
+        Returns a list of ``plans`` that each have the following shape:
+
+        .. vale off
+        .. code-block:: json
+
+            "plan": {
+                "active": true,
+                "bgp_enabled": true,
+                "cdate" "1970-01-01T01:01:01.000Z",
+                "company_id": 111111,
+                "description": "A description of this plan",
+                "deviceTypes": [
+                    {"device_type": "router"},
+                    {"device_type": "host-nprobe-dns-www"}
+                ],
+                "devices": [
+                    {
+                        "id": "111111",
+                        "device_name": "rt0.city.tld.internal",
+                        "device_type": "router"
+                    },
+                ],
+                "edate": "2999-01-01T09:09:09.000Z",
+                "fast_retention": 10,
+                "full_retention": 5,
+                "id": 11111,
+                "max_bigdata_fps": 100,
+                "max_devices": 9001,
+                "max_fps": 200,
+                "name": "KENTIK-PLAN-01",
+                "metadata": {},
+            }
+        .. vale on
+        """
         return self._send_request("GET", "v5/plans")["plans"]
 
     def get_plan(self, plan_id: int) -> dict[str, Any]: