[Search] Add Legacy App Search Gated Form (elastic#189816)

## Summary

This PR adds Gated form and logic when user visits App Search , when
`kibana_uis_enabled == false` and the `role_type` is `owner`. The user
will not be able to able to access any other App Search routes other
than Engines Overview page until this form is submitted.

Also - removes App Search from the search providers so it will no longer
show up in the results.

(note - any migrated clusters will automatically allow access without
the gate on the backend - that is, it will already have set
`kibana_uis_enabled=true`)

Also updates a couple of links and CTA for Workplace Search to be
consistent with new App Search ones.

**Screen Recording:**


https://github.com/user-attachments/assets/8e3d73b3-52d4-4952-bb1e-49219c8cdaed

### Checklist

Delete any items that are not applicable to this PR.

- [x] 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)
- [x] [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
- [x] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [x] 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))
- [x] 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))
- [x] 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)

---------

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

x-pack/plugins/enterprise_search/common/__mocks__/initial_app_data.ts

@@ -41,6 +41,7 @@ export const DEFAULT_INITIAL_APP_DATA = {
   },
   appSearch: {
     accountId: 'some-id-string',
+    kibanaUIsEnabled: true,
     onboardingComplete: true,
     role: {
       id: 'account_id:somestring|user_oid:somestring',

x-pack/plugins/enterprise_search/common/types/app_search.ts

@@ -7,6 +7,7 @@
 
 export interface Account {
   accountId: string;
+  kibanaUIsEnabled: boolean;
   onboardingComplete: boolean;
   role: {
     id: string;

x-pack/plugins/enterprise_search/public/applications/app_search/app_logic.test.ts

@@ -30,10 +30,12 @@ describe('AppLogic', () => {
     },
     account: {
       accountId: 'some-id-string',
+      kibanaUIsEnabled: true,
       onboardingComplete: true,
       role: DEFAULT_INITIAL_APP_DATA.appSearch.role,
     },
     myRole: {},
+    showGateForm: false,
   };
 
   it('sets values from props', () => {
@@ -48,6 +50,7 @@ describe('AppLogic', () => {
       },
       account: {
         accountId: 'some-id-string',
+        kibanaUIsEnabled: true,
         onboardingComplete: true,
         role: DEFAULT_INITIAL_APP_DATA.appSearch.role,
       },
@@ -60,6 +63,7 @@ describe('AppLogic', () => {
         canViewAccountCredentials: true,
         // Truncated for brevity - see utils/role/index.test.ts for full output
       }),
+      showGateForm: false,
     });
   });
 

x-pack/plugins/enterprise_search/public/applications/app_search/app_logic.ts

@@ -16,10 +16,12 @@ import { ConfiguredLimits, Account, Role } from './types';
 import { getRoleAbilities } from './utils/role';
 
 interface AppValues {
-  configuredLimits: ConfiguredLimits;
   account: Account;
+  showGateForm: boolean;
+  configuredLimits: ConfiguredLimits;
   myRole: Role;
 }
+
 interface AppActions {
   setOnboardingComplete(): boolean;
 }
@@ -41,6 +43,10 @@ export const AppLogic = kea<MakeLogicType<AppValues, AppActions, Required<Initia
       },
     ],
     configuredLimits: [props.configuredLimits.appSearch, {}],
+    showGateForm: [
+      props.appSearch.kibanaUIsEnabled === false && props.appSearch.role.roleType === 'owner',
+      {},
+    ],
   }),
   selectors: {
     myRole: [