[Doc][4/N] Reorganize API Reference (#11843)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

docs/source/api/params.md

@@ -0,0 +1,22 @@
+# Optional Parameters
+
+Optional parameters for vLLM APIs.
+
+(sampling-params)=
+
+## Sampling Parameters
+
+```{eval-rst}
+.. autoclass:: vllm.SamplingParams
+    :members:
+```
+
+(pooling-params)=
+
+## Pooling Parameters
+
+```{eval-rst}
+.. autoclass:: vllm.PoolingParams
+    :members:
+```
+