Support for `.gitignore` with `.jj` (Jujutsu VCS) repositories

[gbirke]

I'm currently using Jujutsu VCS, a Git-compatible VCS that uses .gitignore files. I use it without its co-location feature (which places a .git directory in the project root). Instead, I only have a .jj directory in my project root. It would be nice if fd could look for both .git and .jj directories to determine if it should observe the .gitignore file.

The workaround, using --no-require-git, is a bit cumbersome.