Expose `Config.workdir` property.

This is a useful proxy to avoid using `Config.get('workdir')` string
lookup.

platypush/config/__init__.py

@@ -460,6 +460,16 @@ class Config:
         """
         return cls._get_instance(cfgfile, force_reload=True)
 
+    @classmethod
+    @property
+    def workdir(cls) -> str:
+        """
+        :return: The path of the configured working directory.
+        """
+        workdir = cls._get_instance().get('workdir')
+        assert workdir
+        return workdir  # type: ignore
+
     @classmethod
     def get(cls, key: Optional[str] = None):
         """