Add retry for VATSIM services

[sentry-io]

Sentry Issue: VATPRC-UNIAPI-12

Flurl.Http.FlurlHttpException: Call failed with status code 500 (Internal Server Error): GET https://api.vatsim.net/v2/members/1889002
  File "FlurlClient.cs", line 337, in async Task<IFlurlResponse> FlurlClient.HandleExceptionAsync(FlurlCall call, Exception ex, CancellationToken token)
    throw ex;
  File "FlurlClient.cs", line 183, in async Task<IFlurlResponse> FlurlClient.SendAsync(IFlurlRequest request, HttpCompletionOption completionOption, CancellationToken cancellationToken) x 2
    return await HandleExceptionAsync(call, ex, cancellationToken).ConfigureAwait(false);
  File "ResponseExtensions.cs", line 21, in async Task<T> ResponseExtensions.ReceiveJson<T>(Task<IFlurlResponse> response)
    using var resp = await response.ConfigureAwait(false);
  File "Services/VatsimService.cs", line 36, in async Task<UserInfo> VatsimService.GetUserInfo(string cid, CancellationToken ct)+(?) => { }
  File "Services/VatsimService.cs", line 33, in async Task<UserInfo> VatsimService.GetUserInfo(string cid, CancellationToken ct)
...
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