Echo: mechanism for collecting custom events lazily (#20365)

* Introduce Echo for collecting frontend metrics

* Update public/app/core/services/echo/Echo.ts

Co-Authored-By: Peter Holmberg <peterholmberg@users.noreply.github.com>

* Custom meta when adding event

* Rename consumer to backend

* Remove buffer from Echo

* Minor tweaks

* Update package.json

* Update public/app/app.ts

* Update public/app/app.ts

* Collect paint metrics when collecting tti. Remove echoBackendFactory

* Update yarn.lock

* Move Echo interfaces to runtime

* progress on meta and echo

* Collect meta analytics events

* Move MetaanalyticsBackend to enterprise repo

* Fixed unit tests

* Removed unused type from test

* Fixed issues with chunk loading (reverted index-template changes)

* Restored changes

* Fixed webpack prod

scripts/webpack/webpack.dev.js

@@ -81,7 +81,7 @@ module.exports = (env = {}) =>
       new HtmlWebpackPlugin({
         filename: path.resolve(__dirname, '../../public/views/index.html'),
         template: path.resolve(__dirname, '../../public/views/index-template.html'),
-        inject: 'body',
+        inject: false,
         chunksSortMode: 'none',
         excludeChunks: ['dark', 'light']
       }),