[Nightly] Nightly pre-build image (#7388)

### What this PR does / why we need it?
This pull request refactor nightly image build and simplify the logic of
multi workflows.
1. Nightly image build become the prerequisite when the test are
triggered by `schedule` or `workflow_dispatch`
2. Simplify the pull request select case logic
3. Next step: Implement replaceable nightly tests. Specifically, if
nightly tests are manually triggered, they can accept any optional
docker image to meet the needs of different commits(Which means the
image is customizable).
### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.17.0
- vLLM main:
4034c3d32e

---------

Signed-off-by: wangli <wangli858794774@gmail.com>

.github/workflows/_e2e_nightly_single_node.yaml

@@ -40,10 +40,7 @@ on:
         required: false
         type: string
         default: "v0.18.0"
-      is_pr_test:
-        required: true
-        type: boolean
-      is_run:
+      should_run:
         required: true
         type: boolean
 
@@ -64,7 +61,7 @@ jobs:
   e2e-nightly:
     name: ${{ inputs.name || inputs.config_file_path || inputs.tests }}
     runs-on: ${{ inputs.runner }}
-    if: ${{ inputs.is_run }}
+    if: ${{ inputs.should_run }}
     timeout-minutes: 600
     container:
       image: ${{ inputs.image }}
@@ -85,14 +82,14 @@ jobs:
           pip install uv
       
       - name: uninstall vlm vllm-ascend and remove code (if pr test)
-        if: ${{ inputs.is_pr_test }}
+        if: ${{ github.event_name == 'pull_request' }}
         run: |
           pip uninstall -y vllm vllm-ascend || true
           cp -r /vllm-workspace/vllm-ascend/benchmark /tmp/aisbench-backup || true
           rm -rf /vllm-workspace/vllm /vllm-workspace/vllm-ascend
 
       - name: Checkout vllm-project/vllm repo
-        if: ${{ inputs.is_pr_test }}
+        if: ${{ github.event_name == 'pull_request' }}
         uses: actions/checkout@v6
         with:
           repository: vllm-project/vllm
@@ -101,27 +98,27 @@ jobs:
           fetch-depth: 1
 
       - name: Checkout vllm-project/vllm-ascend repo
-        if: ${{ inputs.is_pr_test }}
+        if: ${{ github.event_name == 'pull_request' }}
         uses: actions/checkout@v6
         with:
           path: ./temp-vllm-ascend
           fetch-depth: 1
 
       - name: Move code to /vllm-workspace
-        if: ${{ inputs.is_pr_test }}
+        if: ${{ github.event_name == 'pull_request' }}
         run: |
           mv ./temp-vllm /vllm-workspace/vllm
           mv ./temp-vllm-ascend /vllm-workspace/vllm-ascend
           ls -R /vllm-workspace
 
       - name: Install vllm-project/vllm from source
-        if: ${{ inputs.is_pr_test }}
+        if: ${{ github.event_name == 'pull_request' }}
         working-directory: /vllm-workspace/vllm
         run: |
           VLLM_TARGET_DEVICE=empty uv pip install -e .
       
       - name: Install vllm-project/vllm-ascend
-        if: ${{ inputs.is_pr_test }}
+        if: ${{ github.event_name == 'pull_request' }}
         working-directory: /vllm-workspace/vllm-ascend
         env:
           PIP_EXTRA_INDEX_URL: https://mirrors.huaweicloud.com/ascend/repos/pypi
@@ -132,7 +129,7 @@ jobs:
           uv pip install -v -e .
 
       - name: Install aisbench
-        if: ${{ inputs.is_pr_test }}
+        if: ${{ github.event_name == 'pull_request' }}
         shell: bash -l {0}
         run: |
           cp -r /tmp/aisbench-backup /vllm-workspace/vllm-ascend/benchmark