Support for GitHub Alerts

There's a similar proposal (#1240), but it's from 2019 and doesn't talk about making them like GitHub does.

Describe your feature request

Support for using GitHub Alerts in the application: create shortcuts (like @tip or @warning) to create them and display them as in GitHub markdown files. This doesn't need to be enabled by default, because I know it's not an "original" feature of Markdown.

What problem does this feature solve?

I think this is better for simplifying the work of people who use the application as an editor for files that are then pushed to a GitHub repository (like documentation, README's, etc.).