[releases/v0.18.0][Doc][Misc] Modifying Configuration Parameters (#8618)

### What this PR does / why we need it?
This PR renames the environment variable VLLM_NIXL_ABORT_REQUEST_TIMEOUT
to VLLM_MOONCAKE_ABORT_REQUEST_TIMEOUT to align with the Mooncake
connector naming convention. It also updates the documentation and test
configurations to reflect this change and adjusts the suggested timeout
value in the documentation to 480 seconds for consistency.

### Does this PR introduce _any_ user-facing change?
Yes. The environment variable for configuring the abort request timeout
has been renamed. Users should update their environment settings from
VLLM_NIXL_ABORT_REQUEST_TIMEOUT to VLLM_MOONCAKE_ABORT_REQUEST_TIMEOUT.

### How was this patch tested?
The changes were verified by updating the corresponding test
configuration files and ensuring consistency across the documentation.

---------

Signed-off-by: herizhen <1270637059@qq.com>
Signed-off-by: herizhen <59841270+herizhen@users.noreply.github.com>

tests/e2e/nightly/multi_node/config/DeepSeek-R1-W8A8-longseq.yaml

@@ -13,7 +13,7 @@ env_common:
   HCCL_DETERMINISTIC: True
   TASK_QUEUE_ENABLE: 1
   HCCL_OP_RETRY_ENABLE: "L0:0, L1:0"
-  VLLM_NIXL_ABORT_REQUEST_TIMEOUT: 300000
+  VLLM_MOONCAKE_ABORT_REQUEST_TIMEOUT: 480
 
 disaggregated_prefill:
   enabled: true

tests/e2e/nightly/multi_node/config/DeepSeek-V3_2-W8A8-EP-aime2025.yaml

@@ -15,7 +15,7 @@ env_common:
   ASCEND_TRANSPORT_PRINT: 1
   ACL_OP_INIT_MODE: 1
   ASCEND_A3_ENABLE: 1
-  VLLM_NIXL_ABORT_REQUEST_TIMEOUT: 300000
+  VLLM_MOONCAKE_ABORT_REQUEST_TIMEOUT: 480
   VLLM_ENGINE_READY_TIMEOUT_S: 1800
   HCCL_CONNECT_TIMEOUT: 1200
   HCCL_INTRA_PCIE_ENABLE: 1

tests/e2e/nightly/multi_node/config/DeepSeek-V3_2-W8A8-EP.yaml

@@ -15,7 +15,7 @@ env_common:
   ASCEND_TRANSPORT_PRINT: 1
   ACL_OP_INIT_MODE: 1
   ASCEND_A3_ENABLE: 1
-  VLLM_NIXL_ABORT_REQUEST_TIMEOUT: 300000
+  VLLM_MOONCAKE_ABORT_REQUEST_TIMEOUT: 480
   VLLM_ENGINE_READY_TIMEOUT_S: 1800
   HCCL_CONNECT_TIMEOUT: 1200
   HCCL_INTRA_PCIE_ENABLE: 1