When more than one instance of the same PipelineOption subclass is detected, use the first one. (#36704)

Author: tvalentyn

sdks/python/apache_beam/options/pipeline_options.py

@@ -508,7 +508,7 @@ def get_all_options(
     subset = {}
     parser = _BeamArgumentParser(allow_abbrev=False)
     for cls in PipelineOptions.__subclasses__():
-      subset[str(cls)] = cls
+      subset.setdefault(str(cls), cls)
     for cls in subset.values():
       cls._add_argparse_args(parser)  # pylint: disable=protected-access
     if add_extra_args_fn: