Move gke_cluster_dropdowns to create_cluster dir

This commit creates a create_cluster directory to collect
all Vue applications related to creating kubernetes applications
using gitlab.

It also moves the gke_cluster_dropdowns collection of apps to
the create_cluster directory. gke_cluster_dropdowns contains
dropdown components used to select configuration options to
create a Kubernetes cluster in Google Cloud.

app/assets/javascripts/pages/admin/clusters/index.js

 import PersistentUserCallout from '~/persistent_user_callout';
-import initGkeDropdowns from '~/projects/gke_cluster_dropdowns';
+import initGkeDropdowns from '~/create_cluster/gke_cluster';
 function initGcpSignupCallout() {
   const callout = document.querySelector('.gcp-signup-offer');

app/assets/javascripts/pages/groups/index.js

 import PersistentUserCallout from '~/persistent_user_callout';
-import initGkeDropdowns from '~/projects/gke_cluster_dropdowns';
+import initGkeDropdowns from '~/create_cluster/gke_cluster';
 function initGcpSignupCallout() {
   const callout = document.querySelector('.gcp-signup-offer');

app/assets/javascripts/pages/projects/index.js

-import initGkeDropdowns from '~/projects/gke_cluster_dropdowns';
+import initGkeDropdowns from '~/create_cluster/gke_cluster';
 import initGkeNamespace from '~/projects/gke_cluster_namespace';
 import PersistentUserCallout from '../../persistent_user_callout';
 import Project from './project';

spec/javascripts/projects/gke_cluster_dropdowns/components/gke_machine_type_dropdown_spec.js → spec/javascripts/create_cluster/gke_cluster/components/gke_machine_type_dropdown_spec.js

 import Vue from 'vue';
-import GkeMachineTypeDropdown from '~/projects/gke_cluster_dropdowns/components/gke_machine_type_dropdown.vue';
-import { createStore } from '~/projects/gke_cluster_dropdowns/store';
+import GkeMachineTypeDropdown from '~/create_cluster/gke_cluster/components/gke_machine_type_dropdown.vue';
+import { createStore } from '~/create_cluster/gke_cluster/store';
 import {
   SET_PROJECT,
   SET_PROJECT_BILLING_STATUS,
   SET_ZONE,
   SET_MACHINE_TYPES,
-} from '~/projects/gke_cluster_dropdowns/store/mutation_types';
+} from '~/create_cluster/gke_cluster/store/mutation_types';
 import { mountComponentWithStore } from 'spec/helpers/vue_mount_component_helper';
 import {
   selectedZoneMock,

spec/javascripts/projects/gke_cluster_dropdowns/components/gke_project_id_dropdown_spec.js → spec/javascripts/create_cluster/gke_cluster/components/gke_project_id_dropdown_spec.js

 import Vue from 'vue';
-import GkeProjectIdDropdown from '~/projects/gke_cluster_dropdowns/components/gke_project_id_dropdown.vue';
-import { createStore } from '~/projects/gke_cluster_dropdowns/store';
-import { SET_PROJECTS } from '~/projects/gke_cluster_dropdowns/store/mutation_types';
+import GkeProjectIdDropdown from '~/create_cluster/gke_cluster/components/gke_project_id_dropdown.vue';
+import { createStore } from '~/create_cluster/gke_cluster/store';
+import { SET_PROJECTS } from '~/create_cluster/gke_cluster/store/mutation_types';
 import { mountComponentWithStore } from 'spec/helpers/vue_mount_component_helper';
 import { emptyProjectMock, selectedProjectMock } from '../mock_data';

spec/javascripts/projects/gke_cluster_dropdowns/components/gke_zone_dropdown_spec.js → spec/javascripts/create_cluster/gke_cluster/components/gke_zone_dropdown_spec.js

 import Vue from 'vue';
-import GkeZoneDropdown from '~/projects/gke_cluster_dropdowns/components/gke_zone_dropdown.vue';
-import { createStore } from '~/projects/gke_cluster_dropdowns/store';
+import GkeZoneDropdown from '~/create_cluster/gke_cluster/components/gke_zone_dropdown.vue';
+import { createStore } from '~/create_cluster/gke_cluster/store';
 import {
   SET_PROJECT,
   SET_ZONES,
   SET_PROJECT_BILLING_STATUS,
-} from '~/projects/gke_cluster_dropdowns/store/mutation_types';
+} from '~/create_cluster/gke_cluster/store/mutation_types';
 import { mountComponentWithStore } from 'spec/helpers/vue_mount_component_helper';
 import { selectedZoneMock, selectedProjectMock, gapiZonesResponseMock } from '../mock_data';