[FLINK-38094][python] Introduce pyflink.__version__

Author: Myasuka

flink-python/pyflink/__init__.py

@@ -25,6 +25,8 @@
         'Python versions prior to 3.6 are not supported for PyFlink [' +
         str(sys.version_info) + '].')
 
+from pyflink.version import __version__
+
 
 def keyword(func):
     """
@@ -50,3 +52,7 @@ def add_version_doc(f, version):
     indents = indent_p.findall(original_doc)
     indent = ' ' * (min(len(indent) for indent in indents) if indents else 0)
     f.__doc__ = original_doc.rstrip() + "\n\n%s.. versionadded:: %s" % (indent, version)
+
+__all__ = [
+    "__version__",
+]