Adds fleet status endpoint

Adds an endpoint to retrieve fleet status information.

This endpoint uses a Tesla API proxy to fetch the fleet status
based on provided VINs. It handles authentication using a bearer
token and sends a POST request to the /api/1/vehicles/fleet_status
endpoint.

Also introduces new data models to properly serialize/deserialize the fleet status response.

Source/ProofOfConcept/Models/FleetResponse.cs

@@ -0,0 +1,25 @@
+namespace ProofOfConcept.Models;
+
+using System.Collections.Generic;
+using System.Text.Json.Serialization;
+
+public class FleetRootResponse
+{
+    [JsonPropertyName("response")] public FleetResponse FleetResponse { get; set; } = new FleetResponse();
+}
+
+public class FleetResponse
+{
+    [JsonPropertyName("key_paired_vins")] public List<string> KeyPairedVins { get; set; } = new List<string>();
+    [JsonPropertyName("unpaired_vins")] public List<string> UnpairedVins { get; set; } = new List<string>();
+    [JsonPropertyName("vehicle_info")] public Dictionary<string, VehicleInfo> VehicleInfo { get; set; } = new Dictionary<string, VehicleInfo>();
+}
+
+public class VehicleInfo
+{
+    [JsonPropertyName("firmware_version")] public string FirmwareVersion { get; set; } = "";
+    [JsonPropertyName("vehicle_command_protocol_required")] public bool VehicleCommandProtocolRequired { get; set; }
+    [JsonPropertyName("discounted_device_data")] public bool DiscountedDeviceData { get; set; }
+    [JsonPropertyName("fleet_telemetry_version")] public string FleetTelemetryVersion { get; set; } = "";
+    [JsonPropertyName("total_number_of_keys")] public int TotalNumberOfKeys { get; set; }
+}