[backport core/1.36] CI: Use custom container for E2E tests (#7982)

Backport of #7625 to `core/1.36`

Automatically created by backport workflow.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7982-backport-core-1-36-CI-Use-custom-container-for-E2E-tests-2e76d73d36508150a21de5f6f1e0a49f)
by [Unito](https://www.unito.io)

Co-authored-by: Johnpaul Chiwetelu <49923152+Myestery@users.noreply.github.com>
Co-authored-by: github-actions <github-actions@github.com>

.github/actions/start-comfyui-server/action.yml

@@ -0,0 +1,23 @@
+name: Start ComfyUI Server
+description: 'Start ComfyUI server in a container environment (assumes ComfyUI is pre-installed)'
+
+inputs:
+  front_end_root:
+    description: 'Path to frontend dist directory'
+    required: false
+    default: '$GITHUB_WORKSPACE/dist'
+  timeout:
+    description: 'Timeout in seconds for server startup'
+    required: false
+    default: '600'
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Copy devtools and start server
+      shell: bash
+      run: |
+        set -euo pipefail
+        cp -r ./tools/devtools/* /ComfyUI/custom_nodes/ComfyUI_devtools/
+        cd /ComfyUI && python3 main.py --cpu --multi-user --front-end-root "${{ inputs.front_end_root }}" &
+        wait-for-it --service 127.0.0.1:8188 -t ${{ inputs.timeout }}