util: add types module defining PathLike type

Add a simple new module meant to define types that are commonly
used throughout the code-base. For starters, define `PathLike`
meant to represent file system paths, i.e. strings, bytes, or
anything that provides the `os.PathLike` protocol, i.e. that
can be used with `os.fspath`.

osbuild/util/types.py

@@ -0,0 +1,11 @@
+#
+# Define some useful typing abbreviations
+#
+
+import os
+
+from typing import Union
+
+
+#: Represents a file system path. See also `os.fspath`.
+PathLike = Union[str, bytes, os.PathLike]