[Misc] Refactor additional_config (#1029)

More and more config options are added to additional_config. This PR
provide a new AscendConfig to manage these config options by an easier
way to make code cleaner and readable.

 This PR also added the `additional_config` doc for users.

Added the test_ascend_config.py to make sure the new AscendConfig works
as expect.

TODO: Add e2e test with torchair and deepseek once the CI resource is
available.

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

examples/dp_offline/data_parallel.py

@@ -62,7 +62,9 @@ def main():
               max_num_seqs=num_seqs,
               additional_config={
                   'expert_tensor_parallel_size': etp_size,
-                  'enable_graph_mode': False,
+                  'torchair_graph_config': {
+                      'enabled': False,
+                  },
               })
 
     outputs = llm.generate(prompts, sampling_params)