Ecosystem File with dynamic process name with cluster mode

What's going wrong?

I need to name my processes dynamically according to their indexes in cluster mode.

How could we reproduce this issue?

I have a process that is called "app" and I instantiate it with an ecosystem file like so:

module.exports = {
    apps : [{
        name   : "app",
        script : "./app.js",
        merge_logs: true,
        instances : "-1",
        exec_mode : "cluster"
    }] 
}

What I wanted to do is that PM2 instantiated each of the "app" instances with a different name on the logs and not all with the same name. Like app1, app2, app3, and so on. Is it possible?

Supporting information

pm2 version : 3.5.1
node version : 12.13.0

The issue provides an ecosystem configuration and app.js as the reproduction. Start by checking how PM2 handles name and instances in cluster mode, then determine whether per-instance names are supported. Done would be a documented or implemented way to produce distinct names such as app1, app2, and app3.