How to create a web application with installable plugins/integration like Slack (I don't know the technical term)

I have only worked on RESTApi. But I'm interested in Fullstack development, So I started learning myself, and now I'm working with ReactJS, NodeJS, PHP.

Now I'm curious to know the logic or architecture of installable plugins or integrations (App directory or App store) packages like the Slack app store on the web applications.

I have the interest to recreate these apps (Images): HappyFox App Directory Mattermost

My Questions:

1. Is it possible to create with NodeJS or I need to work with Python or GOLang?
2. Where do I need to start?
3. What is the logic behind this?
4. What is the technical name for this?