[UI] Hedy rules in CodeMirror

[hasan-sh]

Idea incl level
We want to apply indentation based on the commands the user types. Check #4832 (review) for more info.

Additional context
I said "rules" just because this may not only be for indentation, but also other things. For instance, other code editors suggest commands when users click on tab and/or even autocomplete them; i.e., a for loop/function with a snippet of how it's used for a given level. Not sure if we need to, but for now, it's indentation only!

[Felienne]

I think this is a very interesting idea, but more of a discussion than an issue. Because there is potentially a tension between helping the user and teaching them things. I think this would be great for a BSc or maybe even MSc project where the student would explore how this feature would affect students, but not something we want to implement without a bit of exploration.