[Main2Main][Deps][Misc] Upgrade vLLM to v0.15.0 (#6470)

### What this PR does / why we need it?
This PR upgrades the vLLM dependency from `v0.14.1` to `v0.15.0`. This
involves:
- Updating the `VLLM_TAG` in all `Dockerfile`.
- Updating the vLLM version in `docs/source/conf.py`.
- Removing conditional code paths specific to `v0.14.1` across the
codebase, which simplifies maintenance.
- Fix `TypeError: MMEncoderAttention.__init__() got an unexpected
keyword argument 'multimodal_config'` due to
https://github.com/vllm-project/vllm/pull/31972.
- Fix `_shared_experts: 'NoneType' object is not callable` due to
https://github.com/vllm-project/vllm/pull/32082 by
https://github.com/vllm-project/vllm-ascend/pull/6335.
- Fix `ReshapeAndCacheOperation setup failed!` due to
https://github.com/vllm-project/vllm/pull/25954 by overriding attention
metadata slots.

This upgrade is necessary to keep the project aligned with the latest
features, bug fixes, and API changes in the vLLM project.

### Does this PR introduce _any_ user-facing change?
No, this is an internal dependency update and does not introduce any
user-facing changes.

### How was this patch tested?
CI is expected to pass with these changes, ensuring that all existing
tests are successful with the new vLLM version.

- vLLM version: v0.14.1
- vLLM main:
dc917cceb8


co-authored-by: shen-shanshan <467638484@qq.com>

---------

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

.github/workflows/schedule_test_benchmarks.yaml

@@ -51,7 +51,7 @@ jobs:
     strategy:
       matrix:
         include:
-          - vllm_branch: v0.14.1
+          - vllm_branch: v0.15.0
             vllm_ascend_branch: main
       max-parallel: 1
     container:
@@ -130,7 +130,7 @@ jobs:
       - name: Generate step summary
         if: github.event_name != 'schedule' && github.event_name != 'workflow_dispatch'
         run: |
-          cat ./benchmarks/results/benchmark_results.md >> $GITHUB_STEP_SUMMARY
+          cat ./benchmarks/results/benchmark_results.md >> "$GITHUB_STEP_SUMMARY"
 
       - name: Upload benchmark artifacts
         if: github.event_name != 'schedule' && github.event_name != 'workflow_dispatch'
@@ -172,9 +172,9 @@ jobs:
             commit_id=${line%% *}
             commit_title=${line#* }
 
-            git checkout $commit_id
-            commit_time=$(git show -s --format=%cd $commit_hash --date=iso-strict)
-            commit_time_no_tz=${commit_time::19}
+            git checkout "$commit_id"
+            commit_time=$(git show -s --format=%cd "$commit_id" --date=iso-strict)
+            commit_time_no_tz="${commit_time::19}"
             pip install -e .
 
             echo "------------------------"
@@ -191,9 +191,9 @@ jobs:
               ERROR_MSG="Benchmark failed to run"
             fi
             # send the result to es
-            escli add --vllm_branch ${{ matrix.vllm_branch }} \
-            --vllm_ascend_branch ${{ matrix.vllm_ascend_branch }} \
-            --commit_id $commit_id \
+            escli add --vllm_branch "${{ matrix.vllm_branch }}" \
+            --vllm_ascend_branch "${{ matrix.vllm_ascend_branch }}" \
+            --commit_id "$commit_id" \
             --commit_title "$commit_title" \
             --created_at "$commit_time_no_tz" \
             --res_dir ./benchmarks/results \