feat(auth): add support for managing custom headers in auth files

Closes #2457

internal/store/gitstore.go

@@ -446,6 +446,7 @@ func (s *GitTokenStore) readAuthFile(path, baseDir string) (*cliproxyauth.Auth,
 	if email, ok := metadata["email"].(string); ok && email != "" {
 		auth.Attributes["email"] = email
 	}
+	cliproxyauth.ApplyCustomHeadersFromMetadata(auth)
 	return auth, nil
 }