Initializing Amplitude SDK with user_id to prevent race conditions

[snaptravel-eng]

I have a question about integrating the Amplitude SDK with GTM:
https://github.com/amplitude/GTM-Web-Demo

In the GTM demo, I see that the Amplitude SDK initialization is separate from setting the user_id from GTM. This can lead to race conditions where events are fired before the user_id is set.

I'm wondering if there's a way to set the user_id from GTM so that it's part of the Amplitude SDK initialization

amplitude.getInstance().init("API_KEY", userId); // initializes client with the given userId

https://developers.amplitude.com/docs/javascript#setting-user-id