KavitaStats Cleanup (#695)

* Refactored Stats code to be much cleaner and user better naming.

* Cleaned up the actual http code to use Flurl and to return if the upload was successful or not so we can delete the file where appropriate.

* More refactoring for the stats code to clean it up and keep it consistent with our standards.

* Removed a confusing log statement

* Added support for old api key header from original stat server

* Use the correct endpoint, not the new one.

* Code smell

API/Interfaces/Services/IStatsService.cs

@@ -5,7 +5,7 @@ namespace API.Interfaces.Services
 {
     public interface IStatsService
     {
-        Task PathData(ClientInfoDto clientInfoDto);
-        Task CollectAndSendStatsData();
+        Task RecordClientInfo(ClientInfoDto clientInfoDto);
+        Task Send();
     }
 }