add .k (kcl file type) to extensions.py

[prahaladramji]

This PR add .k file type into extensions.py
This extension is used by files for kcl.

[asottile]

file extensions must be unambiguous. searching this file extension gives me many other things (and curiosly none of them are kcl)

[prahaladramji]

@asottile what is the criteria for this? If it must be unambiguous then i'm guessing it'd be difficult with a single character extension. :).

Would it have been acceptable if i replaced the term from kcl to kcl-lang, which a google search provides exactly the expected result.

The kcl project was recently accepted into the cloud native foundation project.
https://www.cncf.io/projects/kcl/

[asottile]

I searched ".k extension" if that's not unambiguous I can't accept it

[asottile]

it's not my fault the kcl project made a poor decision on their file extension

[prahaladramji]

fair enough, thanks for info.