test: benchmark scripts (#3160)

# What does this PR do?
1. Add our own benchmark script instead of locust (doesn't support
measuring streaming latency well)
2. Simplify k8s deployment
3. Add a simple profile script for locally running server

## Test Plan
❮ ./run-benchmark.sh --target stack --duration 180 --concurrent 10

============================================================
BENCHMARK RESULTS
============================================================
Total time: 180.00s
Concurrent users: 10
Total requests: 1636
Successful requests: 1636
Failed requests: 0
Success rate: 100.0%
Requests per second: 9.09

Response Time Statistics:
  Mean: 1.095s
  Median: 1.721s
  Min: 0.136s
  Max: 3.218s
  Std Dev: 0.762s

Percentiles:
  P50: 1.721s
  P90: 1.751s
  P95: 1.756s
  P99: 1.796s

Time to First Token (TTFT) Statistics:
  Mean: 0.037s
  Median: 0.037s
  Min: 0.023s
  Max: 0.211s
  Std Dev: 0.011s

TTFT Percentiles:
  P50: 0.037s
  P90: 0.040s
  P95: 0.044s
  P99: 0.055s

Streaming Statistics:
  Mean chunks per response: 64.0
  Total chunks received: 104775

docs/source/distributions/k8s-benchmark/stack-k8s.yaml.template

@@ -44,8 +44,6 @@ spec:
           value: "${SAFETY_MODEL}"
         - name: TAVILY_SEARCH_API_KEY
           value: "${TAVILY_SEARCH_API_KEY}"
-        - name: MOCK_INFERENCE_PORT
-          value: "${MOCK_INFERENCE_PORT}"
         - name: VLLM_URL
           value: http://vllm-server.default.svc.cluster.local:8000/v1
         - name: VLLM_MAX_TOKENS
@@ -54,8 +52,6 @@ spec:
           value: http://vllm-server-safety.default.svc.cluster.local:8001/v1
         - name: VLLM_TLS_VERIFY
           value: "false"
-        - name: MOCK_INFERENCE_MODEL
-          value: "${MOCK_INFERENCE_MODEL}"
         command: ["python", "-m", "llama_stack.core.server.server", "/etc/config/stack_run_config.yaml", "--port", "8323"]
         ports:
           - containerPort: 8323