[BugFix] fix too many open files problem (#3256)

* Update cache_messager.py

* fix too many open files problem

* fix too many open files problem

* fix too many open files problem

* fix ci bugs

* Update api_server.py

* add parameter

* format

* format

* format

* format

* Update parameters.md

* Update parameters.md

* Update serving_completion.py

* Update serving_chat.py

* Update envs.py

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Co-authored-by: Jiang-Jia-Jun <163579578+Jiang-Jia-Jun@users.noreply.github.com>

fastdeploy/envs.py

@@ -84,6 +84,8 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "FD_PLUGINS": lambda: None if "FD_PLUGINS" not in os.environ else os.environ["FD_PLUGINS"].split(","),
     # set trace attribute job_id.
     "FD_JOB_ID": lambda: os.getenv("FD_JOB_ID"),
+    # support max connections
+    "FD_SUPPORT_MAX_CONNECTIONS": lambda: 768,
 }