MM-59854 Fully allow at mentions in message attachment field values and add E2E tests (#28018)

* Add descriptions to test cases for getNeededAtMentionedUsernames

* MM-59854 Load users who are at-mentioned in message attachment fields

* MM-59854 Add server support for at-mentioning users in message attachment fields

* Migrate support/external_commands from JS to TS

* MM-59584 Ensure that at-mentions never show in other message attachment fields

* MM-59584 Add E2E tests for how we load users based on at mentions

* Use new E2E test helpers in other places

* Update snapshots

e2e-tests/cypress/tests/integration/channels/system_console/demoted_user_spec.js

@@ -11,10 +11,8 @@
 // Group: @channels @system_console @smoke
 
 import * as TIMEOUTS from '../../../fixtures/timeouts';
-import {getAdminAccount} from '../../../support/env';
 
 describe('System Console', () => {
-    const sysadmin = getAdminAccount();
     let testUser;
 
     before(() => {
@@ -25,10 +23,8 @@ describe('System Console', () => {
     });
 
     it('MM-T922 Demoted user cannot continue to view System Console', () => {
-        const baseUrl = Cypress.config('baseUrl');
-
         // # Set user to be a sysadmin, so it can access the system console
-        cy.externalRequest({user: sysadmin, method: 'put', baseUrl, path: `users/${testUser.id}/roles`, data: {roles: 'system_user system_admin'}});
+        cy.externalUpdateUserRoles(testUser.id, 'system_user system_admin');
 
         // # Visit a page on the system console
         cy.visit('/admin_console/reporting/system_analytics');
@@ -36,7 +32,7 @@ describe('System Console', () => {
         cy.url().should('include', '/admin_console/reporting/system_analytics');
 
         // # Change the role of the user back to user
-        cy.externalRequest({user: sysadmin, method: 'put', baseUrl, path: `users/${testUser.id}/roles`, data: {roles: 'system_user'}});
+        cy.externalUpdateUserRoles(testUser.id, 'system_user');
 
         // # User should get redirected to town square
         cy.get('#adminConsoleWrapper').should('not.exist');