Encode string request body as utf-8 (#125)

Otherwise, http.client [tries to encode it](https://github.com/python/cpython/blob/v3.9.19/Lib/http/client.py#L166) as `latin-1`.

[ML-7498](https://iguazio.atlassian.net/browse/ML-7498)

tests/test_client.py

@@ -215,37 +215,34 @@ def setUp(self):
         self._delete_dir(self._object_dir)
 
     def test_object(self):
-        contents = "vegans are better than everyone"
+        body = "this unicode character Ě triggers ML-7498"
+        body_bytes = body.encode("utf-8")
 
         response = self._client.object.get(
             container=self._container, path=self._object_path, raise_for_status=v3io.dataplane.RaiseForStatus.never
         )
 
         self.assertEqual(404, response.status_code)
 
-        # put contents to some object
-        self._client.object.put(container=self._container, path=self._object_path, body=contents)
+        # put body to some object
+        self._client.object.put(container=self._container, path=self._object_path, body=body)
 
-        # get the object contents
+        # get the object body
         response = self._client.object.get(container=self._container, path=self._object_path)
-        if not isinstance(response.body, str):
-            response.body = response.body.decode("utf-8")
-        self.assertEqual(response.body, contents)
+        self.assertEqual(response.body, body_bytes)
 
         response = self._client.object.get(container=self._container, path=self._object_path, offset=0, num_bytes=10)
-        if not isinstance(response.body, str):
-            response.body = response.body.decode("utf-8")
-        self.assertEqual(response.body, contents[0:10])
+        self.assertEqual(response.body, body_bytes[0:10])
 
         # get the head of the object
         response = self._client.object.head(container=self._container, path=self._object_path)
 
-        self.assertIn(("Content-Length", str(len(contents))), response.headers.items())
+        self.assertIn(("Content-Length", str(len(body_bytes))), response.headers.items())
 
         # get the head of the dir-object
         response = self._client.object.head(container=self._container, path=self._object_dir)
 
-        self.assertIn(("Content-Length", str(0)), response.headers.items())
+        self.assertIn(("Content-Length", "0"), response.headers.items())
 
         # delete the object
         self._client.object.delete(container=self._container, path=self._object_path)

v3io/dataplane/request.py

@@ -117,13 +117,19 @@ def encode_get_object(container_name, access_key, kwargs):
 
 
 def encode_put_object(container_name, access_key, kwargs):
-    headers = None
+    headers = {
+        "Content-Type": "application-octet-stream",
+    }
 
     # if the append flag is passed, add a range header
     if kwargs["append"]:
         headers = {"Range": "-1"}
 
-    return _encode("PUT", container_name, access_key, kwargs["path"], None, headers, kwargs["body"])
+    body = kwargs["body"]
+    if isinstance(body, str):
+        body = body.encode("utf-8")
+
+    return _encode("PUT", container_name, access_key, kwargs["path"], None, headers, body)
 
 
 def encode_delete_object(container_name, access_key, kwargs):