MM-47288 refactor: convert channels/channel/ files to ts (#28483)

* refactor: convert channels/channel/ files to ts

- convert js files to typescript
- update types
- fix lint issues

Fixes: 21299

* fix: solve lint issues channels/channel

- fix lint issues
- udpate types

* fix: adjustment to test case MM-T1687

- code reorganization for test case MM-T1687

* fix: update types on function apiCreateCustomAdmin

- update types for apiCreateCustomAdmin on  user.d.ts so that
lint issue is solved

e2e-tests/cypress/tests/support/ui/search.ts

@@ -0,0 +1,38 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import {ChainableT} from 'tests/types';
+
+function uiSearchPosts(searchTerm: string) {
+    // # Enter the search terms and hit enter to start the search
+    cy.get('#searchBox').clear().type(searchTerm).type('{enter}');
+
+    // * Wait for the RHS to open and the search results to appear
+    cy.contains('.sidebar--right__header', 'Search Results').should('be.visible');
+    cy.get('#searchContainer .LoadingSpinner').should('not.exist');
+}
+
+Cypress.Commands.add('uiSearchPosts', uiSearchPosts);
+
+function uiJumpToSearchResult(postId: string) {
+    // # Find the post in the search results and click Jump
+    cy.get(`#searchResult_${postId}`).contains('a', 'Jump').click();
+
+    // * Verify the URL changes to the permalink URL
+    cy.url().should((url) => url.endsWith(`/${postId}`));
+
+    // * Verify that the permalinked post is highlighted in the center channel
+    cy.get(`#post_${postId}.post--highlight`).should('be.visible');
+}
+
+Cypress.Commands.add('uiJumpToSearchResult', uiJumpToSearchResult);
+
+declare global {
+    // eslint-disable-next-line @typescript-eslint/no-namespace
+    namespace Cypress {
+        interface Chainable {
+            uiSearchPosts(searchTerm: string): ChainableT;
+            uiJumpToSearchResult(postId: string): ChainableT;
+        }
+    }
+}