use a common dir as default location for configs and downloads

[simontaurus]

osw.express currently uses

osw-python/src/osw/express.py

Line 30 in 5aea370

CREDENTIALS_FP_DEFAULT = BASE_PATH / "osw_files" / CREDENTIALS_FN_DEFAULT

auth.CredentialManager uses the root folder

osw-python/src/osw/auth.py

Line 255 in 5aea370

filepath_ = [Path.cwd() / CREDENTIALS_FN_DEFAULT]

For discussion:
Use the same subfolder , maybe prefixed .osw_files or .osw => keep osw_files as dir name

add osw_files to .gitignore