add vc config dir (#7173)

### Description
Add ability to use Vercel's config dir for whatever we need.

Closes TURBO-2193

Author: Zertsov

crates/turborepo-dirs/src/lib.rs

@@ -12,3 +12,14 @@ pub fn config_dir() -> Option<PathBuf> {
     }
     dirs_config_dir()
 }
+
+/// Returns the path to the user's configuration directory. This is a wrapper
+/// around `dirs_next::config_dir` that also checks the `VERCEL_CONFIG_DIR_PATH`
+/// environment variable. If the environment variable is set, it will return
+/// that path instead of `dirs_next::config_dir`.
+pub fn vercel_config_dir() -> Option<PathBuf> {
+    if let Ok(dir) = std::env::var("VERCEL_CONFIG_DIR_PATH") {
+        return Some(PathBuf::from(dir));
+    }
+    dirs_config_dir()
+}