New: Identify indexers that are already setup in add list

frontend/src/Store/Selectors/createExistingIndexerSelector.js

@@ -0,0 +1,15 @@
+import _ from 'lodash';
+import { createSelector } from 'reselect';
+import createAllIndexersSelector from './createAllIndexersSelector';
+
+function createExistingIndexerSelector() {
+  return createSelector(
+    (state, { definitionName }) => definitionName,
+    createAllIndexersSelector(),
+    (definitionName, indexers) => {
+      return _.some(indexers, { definitionName });
+    }
+  );
+}
+
+export default createExistingIndexerSelector;