Support E2E stress tests in run_tests.js (#29682)

* [skip ci] Adapt run_tests.js for stress testing
* [skip ci] Make channel_read_after_permalink_spec.js retry-able
* [skip ci] Fix ui_commands.ts fix
* [skip ci] Improve postMessageAndWait
* [skip ci] Fix unread_on_public_channel_spec.js
* [skip ci] Demote unread_on_public_channel_spec.js
* Update e2e-tests/README.md

Co-authored-by: Saturnino Abril <5334504+saturninoabril@users.noreply.github.com>

* [skip ci] Fix mesage_reply_bot_post_spec.js

---------

Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Saturnino Abril <5334504+saturninoabril@users.noreply.github.com>

e2e-tests/cypress/tests/integration/channels/messaging/channel_read_after_permalink_spec.js

@@ -18,7 +18,7 @@ describe('Messaging', () => {
     let testUser;
     let otherUser;
 
-    before(() => {
+    beforeEach(() => {
         cy.apiInitSetup().then(({team, channel, user}) => {
             testTeam = team;
             testChannel = channel;

e2e-tests/cypress/tests/integration/channels/messaging/message_reply_bot_post_spec.js

@@ -144,7 +144,7 @@ describe('Messaging', () => {
                     cy.uiCloseRHS();
 
                     // * Verify that the reply is in the channel view with matching text
-                    cy.get(`#post_${replyId}`).within(() => {
+                    cy.get(`#post_${replyId}`).scrollIntoView().within(() => {
                         cy.findByTestId('post-link').should('be.visible').and('have.text', 'Commented on ' + bot.username + 'BOT\'s message: Hello message from ' + bot.username);
                         cy.get(`#postMessageText_${replyId}`).should('be.visible').and('have.text', replyMessage);
                     });

e2e-tests/cypress/tests/integration/channels/notifications/unread_on_public_channel_spec.js

@@ -7,7 +7,6 @@
 // - Use element ID when selecting an element. Create one if none.
 // ***************************************************************
 
-// Stage: @prod
 // Group: @channels @notifications
 
 import * as TIMEOUTS from '../../../fixtures/timeouts';
@@ -18,7 +17,7 @@ describe('Notifications', () => {
     let testTeam;
 
     beforeEach(() => {
-        cy.apiInitSetup().then(({team, user}) => {
+        cy.apiAdminLogin().apiInitSetup().then(({team, user}) => {
             testUser = user;
             testTeam = team;
 
@@ -48,11 +47,6 @@ describe('Notifications', () => {
                     // # Go to test channel
                     cy.visit(`/${team.name}/channels/${channel.name}`);
 
-                    // # Scroll above the last few messages
-                    cy.get('div.post-list__dynamic', {timeout: TIMEOUTS.ONE_MIN}).should('be.visible').
-                        scrollTo(0, '70%', {duration: TIMEOUTS.ONE_SEC}).
-                        wait(TIMEOUTS.ONE_SEC);
-
                     // # scroll to the last channel
                     cy.get('#sidebar-left li').last().scrollIntoView();
                 });
@@ -66,7 +60,11 @@ describe('Notifications', () => {
 
         // # Get last post and reply a message
         cy.getLastPostId().then((postId) => {
+            // # Open the RHS reply form, then scroll above the last few messages
             cy.clickPostCommentIcon(postId);
+            cy.get('div.post-list__dynamic', {timeout: TIMEOUTS.ONE_MIN}).should('be.visible').
+                scrollTo(0, '70%', {duration: TIMEOUTS.ONE_SEC}).
+                wait(TIMEOUTS.ONE_SEC);
             const replyMessage = 'A reply to an older post';
             cy.postMessageReplyInRHS(replyMessage);
         });