How can I get insights into my github app usage?

We are looking to get installation / subscriber counts from the API so we can setup some internal analytics on that info. We want to setup a slack message hook for installation / uninstallation events. I see the installation event as one of the events on github webhooks - Webhook events and payloads - GitHub Docs. But I don’t think this event is available for github apps to subscribe to because I don’t see it on the github app settings → Permissions & Events.

Is there any way we can implement what we are trying to achieve?

I ended up using GitHub Marketplace Webhooks - Webhook events for the GitHub Marketplace API - GitHub Docs
Doesn’t really give subscriber and install counts, but it is still something