feat(ci): support downloading extra app artifacts in pytest

Add app_extra S3 artifact type, extend idf-ci download plumbing, and
expose a download_app_extra pytest fixture for managed_components deps.

tools/ci/idf_ci_utils.py

@@ -12,6 +12,9 @@ from functools import cached_property
 
 IDF_PATH: str = os.path.abspath(os.getenv('IDF_PATH', os.path.join(os.path.dirname(__file__), '..', '..')))
 
+# S3 artifact type for app-dir files outside build_*
+APP_EXTRA_S3_ARTIFACT_TYPE = 'app_extra'
+
 
 def get_submodule_dirs(full_path: bool = False) -> list[str]:
     """