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/Services/MQTTClient.cs

@@ -5,9 +5,9 @@ namespace ProofOfConcept.Services;
 
 public class MQTTClient : IHostedService
 {
-    private ILogger<MQTTClient> logger;
-    private MQTTClientConfiguration configuration;
-    private MQTTServerConfiguration serverConfiguration;
+    private readonly ILogger<MQTTClient> logger;
+    private readonly MQTTClientConfiguration configuration;
+    private readonly MQTTServerConfiguration serverConfiguration;
 
     private readonly IMqttClient client;