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>

scripts/grafana-server/custom.ini

@@ -1,3 +1,4 @@
+
 [security]
 content_security_policy = true
 content_security_policy_template = """require-trusted-types-for 'script'; script-src 'self' 'unsafe-eval' 'unsafe-inline' 'strict-dynamic' $NONCE;object-src 'none';font-src 'self';style-src 'self' 'unsafe-inline' blob:;img-src * data:;base-uri 'self';connect-src 'self' grafana.com ws://$ROOT_PATH wss://$ROOT_PATH;manifest-src 'self';media-src 'none';form-action 'self';"""
@@ -5,6 +6,9 @@ content_security_policy_template = """require-trusted-types-for 'script'; script
 [feature_toggles]
 enable = publicDashboards
 
+[plugins]
+allow_loading_unsigned_plugins=grafana-extensionstest-app,grafana-extensionexample1-app,grafana-extensionexample2-app,
+
 [database]
 type=sqlite3
 wal=true