Delay events until `BrowserClient` is initialised

[similicious]

Summary

The init method of BrowserClient is async. While the initialisation is ongoing, the application can already track events. These events will then not be processed by plugins.

With the dispatchQ in the CoreClient there is already a mechanism to buffer events. However tracked events are only put on the queue while CoreClient is initialising (isReady === false). The queue however is processed when the BrowserClient is done initialising.

Motivations

In our tracking setup we have the issue that events are tracked before the BrowserClient is fully initialised. We rely on a custom plugin to run first to ensure user properties are populated.

[Mercy811]

Hi @similicious, we can add the plugin before init. Once initialization is done, events will also be processed by the plugin.