[docs] Add an `.editorconfig` file (#3220)

Authored by: fstirlitz

.editorconfig

@@ -0,0 +1,8 @@
+root = true
+
+[**.py]
+charset = utf-8
+indent_size = 4
+indent_style = space
+trim_trailing_whitespace = true
+insert_final_newline = true