E2E: Add support for building test plugins (#91873)

* build test apps with webpack

* add extensions test app

* update e2e tests

* remove non-build test apps using amd

* use @grafana/plugin-configs rather than create-plugin config

* Update e2e/plugin-e2e/plugin-e2e-api-tests/as-admin-user/extensions/usePluginComponents.spec.ts

Co-authored-by: Jack Westbrook <jack.westbrook@gmail.com>

* Update package.json

Co-authored-by: Jack Westbrook <jack.westbrook@gmail.com>

* use run dir variable instead of hardcoded path

* add dummy licence file

* add separate step for building test plugins

* support nested plugins

* remove react-router-dom from the externals array

* remove add_mode dev

* lint starlark

* pass license path as env variable

* fix the path

* chore(e2e-plugins): clean up dependencies to match core versions

* refactor(e2e-plugins): prefer extending webpack plugins-config

* docs(e2e-plugins): add basic info to extensions test plugin readme

* update readme

* change dir name from custom plugins to test plugins

* change root readme

* update lockfile

---------

Co-authored-by: Jack Westbrook <jack.westbrook@gmail.com>

package.json

@@ -20,6 +20,8 @@
     "e2e:playwright": "yarn playwright test",
     "e2e:playwright:server": "./e2e/plugin-e2e/start-and-run-suite",
     "e2e:storybook": "PORT=9001 ./e2e/run-suite storybook true",
+    "e2e:plugin:build": "nx run-many -t build --projects='@test-plugins/*'",
+    "e2e:plugin:build:dev": "nx run-many -t dev --projects='@test-plugins/*' --maxParallel=100",
     "test": "jest --notify --watch",
     "test:coverage": "jest --coverage",
     "test:coverage:changes": "jest --coverage --changedSince=origin/main",
@@ -431,7 +433,8 @@
       "packages/*",
       "packages/!(grafana-icons)/**",
       "plugins-bundled/internal/*",
-      "public/app/plugins/*/*"
+      "public/app/plugins/*/*",
+      "e2e/test-plugins/*"
     ]
   },
   "engines": {