[PD] Support logprob & Add failure test (#6558)

scripts/playground/disaggregation/cli-logprob.py

@@ -0,0 +1,22 @@
+prompt = "The capital of taiwan is "
+
+import json
+
+import requests
+
+response = requests.post(
+    "http://0.0.0.0:8000/generate",
+    json={
+        "text": prompt,
+        "sampling_params": {"temperature": 0},
+        "return_logprob": True,
+        "return_input_logprob": True,
+        "logprob_start_len": 0,
+    },
+)
+
+j = response.json()
+input_logprobs = j["meta_info"]["input_token_logprobs"]
+output_logprobs = j["meta_info"]["output_token_logprobs"]
+
+print(len(input_logprobs), len(output_logprobs))