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/Controllers/StatsController.cs

@@ -25,7 +25,7 @@ namespace API.Controllers
         {
             try
             {
-                await _statsService.PathData(clientInfoDto);
+                await _statsService.RecordClientInfo(clientInfoDto);
 
                 return Ok();
             }