Ignore self/cls from required args of class functions in convert_to_openai_tool (#20691)

Removed redundant self/cls from required args of class functions in
_get_python_function_required_args:

```python
class MemberTool:
    def search_member(
            self,
            keyword: str,
            *args,
            **kwargs,
    ):
        """Search on members with any keyword like first_name, last_name, email

        Args:
            keyword: Any keyword of member
        """

        headers = dict(authorization=kwargs['token'])
        members = []
        try:
            members = request_(
                method='SEARCH',
                url=f'{service_url}/apiv1/members',
                headers=headers,
                json=dict(query=keyword),
            )

        except Exception as e:
            logger.info(e.__doc__)

        return members

convert_to_openai_tool(MemberTool.search_member)
```
expected result:
```
{'type': 'function', 'function': {'name': 'search_member', 'description': 'Search on members with any keyword like first_name, last_name, username, email', 'parameters': {'type': 'object', 'properties': {'keyword': {'type': 'string', 'description': 'Any keyword of member'}}, 'required': ['keyword']}}}
```

#20685

---------

Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>
Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/core/tests/unit_tests/utils/test_function_calling.py

@@ -71,6 +71,29 @@ def json_schema() -> Dict:
     }
 
 
+class Dummy:
+    def dummy_function(self, arg1: int, arg2: Literal["bar", "baz"]) -> None:
+        """dummy function
+
+        Args:
+            arg1: foo
+            arg2: one of 'bar', 'baz'
+        """
+        pass
+
+
+class DummyWithClassMethod:
+    @classmethod
+    def dummy_function(cls, arg1: int, arg2: Literal["bar", "baz"]) -> None:
+        """dummy function
+
+        Args:
+            arg1: foo
+            arg2: one of 'bar', 'baz'
+        """
+        pass
+
+
 def test_convert_to_openai_function(
     pydantic: Type[BaseModel],
     function: Callable,
@@ -94,7 +117,15 @@ def test_convert_to_openai_function(
         },
     }
 
-    for fn in (pydantic, function, dummy_tool, json_schema, expected):
+    for fn in (
+        pydantic,
+        function,
+        dummy_tool,
+        json_schema,
+        expected,
+        Dummy.dummy_function,
+        DummyWithClassMethod.dummy_function,
+    ):
         actual = convert_to_openai_function(fn)  # type: ignore
         assert actual == expected