[misc][frontend] log all available endpoints

[youkaichao]

fixes #6194

quite a lot users don't know the difference between simple api server and openai api server. I got several issue reports recently, that users are manually getting /generate from openai api server, or getting /v1/models from simple api server, and then complain about 404 response.

logging all available endpoints should help users clearly know what endpoints they can test.

example output:

simple api server: python -m vllm.entrypoints.api_server

INFO 07-07 13:50:36 api_server.py:116] Available endpoints are:
INFO 07-07 13:50:36 api_server.py:120] Path: /openapi.json, Methods: GET, HEAD
INFO 07-07 13:50:36 api_server.py:120] Path: /docs, Methods: GET, HEAD
INFO 07-07 13:50:36 api_server.py:120] Path: /docs/oauth2-redirect, Methods: GET, HEAD
INFO 07-07 13:50:36 api_server.py:120] Path: /redoc, Methods: GET, HEAD
INFO 07-07 13:50:36 api_server.py:120] Path: /health, Methods: GET
INFO 07-07 13:50:36 api_server.py:120] Path: /generate, Methods: POST

openai api server: python -m vllm.entrypoints.openai.api_server

INFO 07-07 13:53:48 api_server.py:244] Available endpoints are:
INFO 07-07 13:53:48 api_server.py:248] Path: /openapi.json, Methods: HEAD, GET
INFO 07-07 13:53:48 api_server.py:248] Path: /docs, Methods: HEAD, GET
INFO 07-07 13:53:48 api_server.py:248] Path: /docs/oauth2-redirect, Methods: HEAD, GET
INFO 07-07 13:53:48 api_server.py:248] Path: /redoc, Methods: HEAD, GET
INFO 07-07 13:53:48 api_server.py:248] Path: /metrics, Methods: No methods
INFO 07-07 13:53:48 api_server.py:248] Path: /health, Methods: GET
INFO 07-07 13:53:48 api_server.py:248] Path: /tokenize, Methods: POST
INFO 07-07 13:53:48 api_server.py:248] Path: /detokenize, Methods: POST
INFO 07-07 13:53:48 api_server.py:248] Path: /v1/models, Methods: GET
INFO 07-07 13:53:48 api_server.py:248] Path: /version, Methods: GET
INFO 07-07 13:53:48 api_server.py:248] Path: /v1/chat/completions, Methods: POST
INFO 07-07 13:53:48 api_server.py:248] Path: /v1/completions, Methods: POST
INFO 07-07 13:53:48 api_server.py:248] Path: /v1/embeddings, Methods: POST

[comaniac]

LGTM

[youkaichao]

merge as failed tests are caused by hf connection error.