[Index Management][Serverless] Remove primaries and replicas in indices list (#169259)

## Summary

Fixes https://github.com/elastic/kibana/issues/165905 

This PR hides the columns "primaries" and "replicas" in the indices list
on Serverless. I decided to reuse the config value
`xpack.index_management.enableIndexStats` because these values fall
closely together with other hidden columns on Serverless like "health",
"storage size" etc. I also removed the width css for the index name
column in that case to fix the table view, otherwise the column would
stay always the 25% width of the table.

### Screeenshots
<img width="1130" alt="Screenshot 2023-10-18 at 16 00 19"
src="29a9eb83-ad46-48a4-8102-684570f51733">

### How to test 
1. Start ES and Kibana in Serverless mode with `yarn es serverless
--ssl` and `yarn serverless-es --ssl`
2. Navigate to Index Management and toggle the switch to display hidden
indices because those have data stream names.

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/index_management/__jest__/client_integration/home/indices_tab.test.ts

@@ -12,19 +12,11 @@ import { setupEnvironment, nextTick } from '../helpers';
 import { IndicesTestBed, setup } from './indices_tab.helpers';
 import { createDataStreamPayload, createNonDataStreamIndex } from './data_streams_tab.helpers';
 
-/**
- * The below import is required to avoid a console error warn from the "brace" package
- * console.warn ../node_modules/brace/index.js:3999
-      Could not load worker ReferenceError: Worker is not defined
-          at createWorker (/<path-to-repo>/node_modules/brace/index.js:17992:5)
- */
-import { stubWebWorker } from '@kbn/test-jest-helpers';
 import { createMemoryHistory } from 'history';
 import {
   breadcrumbService,
   IndexManagementBreadcrumb,
 } from '../../../public/application/services/breadcrumbs';
-stubWebWorker();
 
 describe('<IndexManagementHome />', () => {
   let testBed: IndicesTestBed;
@@ -399,7 +391,7 @@ describe('<IndexManagementHome />', () => {
         const { table } = testBed;
         const { tableCellsValues } = table.getMetaData('indexTable');
 
-        expect(tableCellsValues).toEqual([['', 'test', '1', '1', '']]);
+        expect(tableCellsValues).toEqual([['', 'test', '']]);
       });
     });
   });

x-pack/plugins/index_management/public/application/sections/home/index_list/index_table/index_table.js

@@ -65,17 +65,15 @@ const getHeaders = ({ showIndexStats }) => {
     headers.status = i18n.translate('xpack.idxMgmt.indexTable.headers.statusHeader', {
       defaultMessage: 'Status',
     });
-  }
 
-  headers.primary = i18n.translate('xpack.idxMgmt.indexTable.headers.primaryHeader', {
-    defaultMessage: 'Primaries',
-  });
+    headers.primary = i18n.translate('xpack.idxMgmt.indexTable.headers.primaryHeader', {
+      defaultMessage: 'Primaries',
+    });
 
-  headers.replica = i18n.translate('xpack.idxMgmt.indexTable.headers.replicaHeader', {
-    defaultMessage: 'Replicas',
-  });
+    headers.replica = i18n.translate('xpack.idxMgmt.indexTable.headers.replicaHeader', {
+      defaultMessage: 'Replicas',
+    });
 
-  if (showIndexStats) {
     headers.documents = i18n.translate('xpack.idxMgmt.indexTable.headers.documentsHeader', {
       defaultMessage: 'Docs count',
     });
@@ -265,13 +263,16 @@ export class IndexTable extends Component {
     const headers = getHeaders({ showIndexStats: config.enableIndexStats });
     return Object.entries(headers).map(([fieldName, label]) => {
       const isSorted = sortField === fieldName;
+      // we only want to make index name column 25% width when there are more columns displayed
+      const widthClassName =
+        fieldName === 'name' && config.enableIndexStats ? 'indTable__header__width' : '';
       return (
         <EuiTableHeaderCell
           key={fieldName}
           onSort={() => this.onSort(fieldName)}
           isSorted={isSorted}
           isSortAscending={isSortAscending}
-          className={'indTable__header--' + fieldName}
+          className={widthClassName}
           data-test-subj={`indexTableHeaderCell-${fieldName}`}
         >
           {label}

x-pack/plugins/index_management/public/index.scss

@@ -11,7 +11,7 @@
 
 .indTable {
   // The index table is a bespoke table and can't make use of EuiBasicTable's width settings
-  thead th.indTable__header--name { // stylelint-disable-line selector-no-qualifying-type
+  thead th.indTable__header__width { // stylelint-disable-line selector-no-qualifying-type
     width: 25%;
   }