Allow specifying MAYAPY exe via environmenti

This matches the logic we have implemented in the
`deadline-cloud-for-cinema-4d` package.

Signed-off-by: Alex Hughes <[email protected]>

src/deadline/maya_adaptor/MayaAdaptor/adaptor.py

@@ -362,7 +362,7 @@ def _start_maya_client(self) -> None:
         Raises:
             FileNotFoundError: If the maya_client.py file could not be found.
         """
-        mayapy_exe = "mayapy"
+        mayapy_exe = os.environ.get("MAYA_ADAPTOR_MAYAPY_EXE", "mayapy")
         regexhandler = RegexHandler(self._get_regex_callbacks())
 
         # Add the openjd namespace directory to PYTHONPATH, so that adaptor_runtime_client