@grafana/e2e: added login credential env vars (#24359)

... for remote instances

packages/grafana-e2e/src/flows/login.ts

 import { e2e } from '../index';
 
-export const login = (username: string, password: string) => {
-  e2e().logToConsole('Trying to login with:', { username, password });
+export const login = (username: string = 'admin', password: string = 'admin') => {
+  e2e().logToConsole('Trying to login with username:', username);
   e2e.pages.Login.visit();
   e2e.pages.Login.username()
     .should('be.visible') // prevents flakiness
@@ -14,5 +14,5 @@ export const login = (username: string, password: string) => {
   e2e()
     .get('.login-page')
     .should('not.exist');
-  e2e().logToConsole('Logged in with', { username, password });
+  e2e().logToConsole('Logged in with username:', username);
 };

packages/grafana-e2e/src/support/scenario.ts

+import { e2e } from '../';
 import { Flows } from '../flows';
 import { getScenarioContext } from './scenarioContext';
 
@@ -23,7 +24,7 @@ export const e2eScenario = ({
       it.skip(itName, () => scenario());
     } else {
       beforeEach(() => {
-        Flows.login('admin', 'admin');
+        Flows.login(e2e.env('USERNAME'), e2e.env('PASSWORD'));
         if (addScenarioDataSource) {
           Flows.addDataSource();
         }