[Refactor]Refactor of vllm_ascend/distributed module (#5719)

### What this PR does / why we need it?
Based on the RFC:https://github.com/vllm-project/vllm-ascend/issues/5604

This PR is a refactoring of vllm_ascend/distributed, moving all
kv_transfer realtaed codes into a dedicated folder, which has already
been done in vLLM

### Does this PR introduce _any_ user-facing change?
NA

### How was this patch tested?


- vLLM version: v0.13.0
- vLLM main:
2f4e6548ef

---------

Signed-off-by: lty <linhebiwen@gmail.com>

docs/source/user_guide/feature_guide/large_scale_ep.md

@@ -163,8 +163,7 @@ vllm serve vllm-ascend/DeepSeek-R1-W8A8 \
       "kv_role": "kv_producer",
       "kv_parallel_size": "1",
       "kv_port": "20001",
-      "engine_id": "0",
-      "kv_connector_module_path": "vllm_ascend.distributed.mooncake_connector"
+      "engine_id": "0"
     }'
     --additional-config '{"enable_weight_nz_layout":true,"enable_prefill_optimizations":true}'
 ```
@@ -230,8 +229,7 @@ vllm serve vllm-ascend/DeepSeek-R1-W8A8 \
         "kv_role": "kv_consumer",
         "kv_parallel_size": "1",
         "kv_port": "20001",
-        "engine_id": "0",
-        "kv_connector_module_path": "vllm_ascend.distributed.mooncake_connector"
+        "engine_id": "0"
         }' \
     --additional-config '{"enable_weight_nz_layout":true}'
 ```
@@ -435,8 +433,7 @@ In the PD separation scenario, we provide a optimized configuration.
       "kv_role": "kv_producer",
       "kv_parallel_size": "1",
       "kv_port": "20001",
-      "engine_id": "0",
-      "kv_connector_module_path": "vllm_ascend.distributed.mooncake_connector"
+      "engine_id": "0"
     }'
 ```
 
@@ -458,8 +455,7 @@ In the PD separation scenario, we provide a optimized configuration.
       "kv_role": "kv_consumer",
       "kv_parallel_size": "1",
       "kv_port": "20001",
-      "engine_id": "0",
-      "kv_connector_module_path": "vllm_ascend.distributed.mooncake_connector"
+      "engine_id": "0"
     }'
 ```