Removes redundant content-type header

Removes the explicit setting of the "Content-Type" header,
as HttpClient handles this automatically based on the content being sent.

This change simplifies the code and avoids potential conflicts
if the content type is already being set elsewhere.

Source/ProofOfConcept/Program.cs

@@ -248,7 +248,6 @@ if (app.Environment.IsDevelopment())
         HttpClient client = httpClientFactory.CreateClient("InsecureClient");
         client.BaseAddress = new Uri("https://tesla_command_proxy");
         client.DefaultRequestHeaders.Add("Authorization", $"Bearer {access_token}");
-        client.DefaultRequestHeaders.Add("Content-Type", "application/json");
         
         //Get cars
         VehiclesEnvelope? vehiclesEnvelope = await client.GetFromJsonAsync<VehiclesEnvelope>("/api/1/vehicles");