[Discover] Unskip Discover customizations Serverless tests (#166407)

## Summary

This PR unskips the Discover customizations Serverless tests. I ran 100x
flaky test runs against each project type to confirm they should no
longer be flaky.

Flaky test runs:
- x100 (`.only`):
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3111
- x100 Search:
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3118
- x100 O11y:
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3144
- x100 Security:
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3153

Resolves #165396.
Resolves #165438.

### Checklist

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [ ] Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [ ] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/test_serverless/functional/test_suites/common/examples/discover_customization_examples/customizations.ts

@@ -12,7 +12,7 @@ const TEST_START_TIME = 'Sep 19, 2015 @ 06:31:44.000';
 const TEST_END_TIME = 'Sep 23, 2015 @ 18:31:44.000';
 
 export default ({ getService, getPageObjects }: FtrProviderContext) => {
-  const PageObjects = getPageObjects(['common', 'timePicker', 'header']);
+  const PageObjects = getPageObjects(['common', 'timePicker', 'header', 'svlCommonPage']);
   const esArchiver = getService('esArchiver');
   const kibanaServer = getService('kibanaServer');
   const testSubjects = getService('testSubjects');
@@ -20,10 +20,10 @@ export default ({ getService, getPageObjects }: FtrProviderContext) => {
   const dataGrid = getService('dataGrid');
   const defaultSettings = { defaultIndex: 'logstash-*' };
 
-  // Flaky in serverless tests (before hook)
-  // Failing: See https://github.com/elastic/kibana/issues/165396
-  describe.skip('Customizations', () => {
+  describe('Customizations', () => {
     before(async () => {
+      // TODO: Serverless tests require login first
+      await PageObjects.svlCommonPage.login();
       await kibanaServer.savedObjects.cleanStandardList();
       await esArchiver.loadIfNeeded('x-pack/test/functional/es_archives/logstash_functional');
       await kibanaServer.importExport.load('test/functional/fixtures/kbn_archiver/discover');