[PS-2507] Enable firefox relay address on creation (#2474)

* Enable firefox relay address on creation

Adding a body (json) to the request and setting enabled to true.
Additionally the description is set to "Generated by Bitwarden." to mimick the behaviour of the other clients

* Add missing encoding and mediaType

* Replace JObject with anonymous type

src/Core/Services/ApiService.cs

@@ -767,6 +767,12 @@ namespace Bit.Core.Services
                         break;
                     case ForwardedEmailServiceType.FirefoxRelay:
                         requestMessage.Headers.Add("Authorization", $"Token {config.ApiToken}");
+                        requestMessage.Content = new StringContent(JsonConvert.SerializeObject(
+                            new
+                            {
+                                enabled = true,
+                                description = "Generated by Bitwarden."
+                            }), Encoding.UTF8, "application/json");
                         break;
                     case ForwardedEmailServiceType.SimpleLogin:
                         requestMessage.Headers.Add("Authentication", config.ApiToken);