Set error.type attribute on failure spans

The semantic conventions mark error.type as Conditionally Required on
failure. For FbException, use the SQLSTATE code; for other exceptions,
use the full exception type name.

Author: fdcastel

src/FirebirdSql.Data.FirebirdClient/Trace/FbActivitySource.cs

@@ -128,6 +128,10 @@ internal static void CommandException(Activity activity, Exception exception, bo
 				? fbException.SQLSTATE
 				: exception.Message;
 
+			activity.SetTag("error.type", exception is FbException fbEx
+				? fbEx.SQLSTATE ?? exception.GetType().FullName
+				: exception.GetType().FullName);
+
 			activity.SetStatus(ActivityStatusCode.Error, errorDescription);
 			activity.Dispose();
 		}