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/enterprise/system_console/reporting/site_statistics_spec.js

@@ -11,7 +11,6 @@
 // Group: @channels @enterprise @system_console
 
 import * as TIMEOUTS from '../../../../../fixtures/timeouts';
-import {getAdminAccount} from '../../../../../support/env';
 
 describe('System Console > Site Statistics', () => {
     let testTeam;
@@ -102,8 +101,6 @@ describe('System Console > Site Statistics', () => {
     it('MM-T902 - Reporting ➜ Site statistics line graphs show same date', () => {
         cy.intercept('**/api/v4/**').as('resources');
 
-        const sysadmin = getAdminAccount();
-
         let newChannel;
 
         // # Create and visit new channel
@@ -114,7 +111,7 @@ describe('System Console > Site Statistics', () => {
         // # Create a bot and get userID
         cy.apiCreateBot().then(({bot}) => {
             const botUserId = bot.user_id;
-            cy.externalRequest({user: sysadmin, method: 'put', path: `users/${botUserId}/roles`, data: {roles: 'system_user system_post_all system_admin'}});
+            cy.externalUpdateUserRoles(botUserId, 'system_user system_post_all system_admin');
 
             // # Get token from bots id
             cy.apiAccessToken(botUserId, 'Create token').then(({token}) => {

e2e-tests/cypress/tests/integration/channels/enterprise/system_console/system_scheme_permission_spec.js

@@ -60,7 +60,7 @@ const setUserTeamAndChannelMemberships = (user, team, channel, channelAdmin = fa
     const admin = getAdminAccount();
 
     // # Set user as regular system user
-    cy.externalRequest({user: admin, method: 'put', path: `users/${user.id}/roles`, data: {roles: 'system_user'}});
+    cy.externalUpdateUserRoles(user.id, 'system_user');
 
     // # Get team membership
     cy.externalRequest({user: admin, method: 'put', path: `teams/${team.id}/members/${user.id}/schemeRoles`, data: {scheme_user: true, scheme_admin: teamAdmin}});

e2e-tests/cypress/tests/integration/channels/enterprise/system_console/team_scheme_permission_spec.js

@@ -91,7 +91,7 @@ const setUserTeamAndChannelMemberships = (user, team, channel, channelAdmin = fa
     const admin = getAdminAccount();
 
     // # Set user as regular system user
-    cy.externalRequest({user: admin, method: 'put', path: `users/${user.id}/roles`, data: {roles: 'system_user'}});
+    cy.externalUpdateUserRoles(user.id, 'system_user');
 
     // # Get team membership
     cy.externalRequest({user: admin, method: 'put', path: `teams/${team.id}/members/${user.id}/schemeRoles`, data: {scheme_user: true, scheme_admin: teamAdmin}});