Common contexts for polling (#13158)

* Common contexts for polling
Don't store contexts on the device array, use the device model
Also should be easier to add different contexts later.

* rename variables for consistency

app/Models/Device.php

@@ -116,6 +116,17 @@ class Device extends BaseModel
         return null;
     }
 
+    /**
+     * Get VRF contexts to poll.
+     * If no contexts are found, return the default context ''
+     *
+     * @return array
+     */
+    public function getVrfContexts(): array
+    {
+        return $this->vrfLites->isEmpty() ? [''] : $this->vrfLites->pluck('context_name')->all();
+    }
+
     /**
      * Get the display name of this device (hostname) unless force_ip_to_sysname is set
      * and hostname is an IP and sysName is set