feat: add git commit hash to Serilog context

PluralKit.API/Startup.cs

@@ -115,7 +115,7 @@ public class Startup
         // add X-PluralKit-Version header
         app.Use((ctx, next) =>
         {
-            ctx.Response.Headers.Add("X-PluralKit-Version", BuildInfoService.Version);
+            ctx.Response.Headers.Add("X-PluralKit-Version", BuildInfoService.FullVersion);
             return next();
         });