add error code to spanner failure logging

Author: itsankit-google

src/main/java/io/cdap/plugin/gcp/spanner/source/SpannerSource.java

@@ -130,8 +130,9 @@ public void configurePipeline(PipelineConfigurer pipelineConfigurer) {
     } catch (SpannerException e) {
       // this is because spanner exception error message is not very user friendly. It contains class names and new
       // lines in the error message.
-      collector.addFailure("Unable to connect to spanner instance.",
-                           "Verify spanner configurations such as instance, database, table, project, etc.")
+      collector.addFailure(String.format(
+          "Unable to connect to spanner instance with error code: %s", e.getErrorCode().name()),
+              "Verify spanner configurations such as instance, database, table, project, etc.")
         .withStacktrace(e.getStackTrace());
     }
   }