MM-62954 E2E/Playwright shared library (#30177)

* feat: Add package.json for Playwright library with dependencies

* feat: Add explicit exports for test.config in playwright-lib package

* feat: Add initialization setup for Mattermost E2E testing with admin and user client

* fix: Update package dependencies and resolve TypeScript build errors

* feat: Update package exports for test.config to support both CommonJS and ESM

* playwright shared library

* add README, fix pipeline

* keep file structures, move report up to playwright

* minimize API, use the prerelease versions of client and types

* bump version

* update package*.json

* resolve merge conflict

* update depedencies and merge conflicts

* update readme and fix ci

* remove unnecessary export and list all external packages

* fix import for Client4

e2e-tests/playwright/test/script/post_install.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+if [ -n "$PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD" ]; then
+    echo "Skipped browsers download for Playwright"
+    exit 0
+fi
+
+# Install needed Playwright browsers only -- chromium and firefox only for these are the ones being used by the tests.
+# May add more browsers in the future.
+# https://playwright.dev/docs/library#browser-downloads
+npx playwright install chromium
+npx playwright install firefox