feat: support stepfun model

[Chi-Kai]

Ⅰ. Describe what this PR did

Support 阶跃星辰(stepfun) model, api documentation (https://platform.stepfun.com)

Ⅱ. Does this pull request fix one issue?

fixes #958

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

envoy.yaml:

# File generated by hgctl. Modify as required.

admin:
  address:
    socket_address:
      protocol: TCP
      address: 0.0.0.0
      port_value: 9901
static_resources:
  listeners:
    - name: listener_0
      address:
        socket_address:
          protocol: TCP
          address: 0.0.0.0
          port_value: 10000
      filter_chains:
        - filters:
            - name: envoy.filters.network.http_connection_manager
              typed_config:
                "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
                scheme_header_transformation:
                  scheme_to_overwrite: https
                stat_prefix: ingress_http
                # Output envoy logs to stdout
                access_log:
                  - name: envoy.access_loggers.stdout
                    typed_config:
                      "@type": type.googleapis.com/envoy.extensions.access_loggers.stream.v3.StdoutAccessLog
                # Modify as required
                route_config:
                  name: local_route
                  virtual_hosts:
                    - name: local_service
                      domains: [ "*" ]
                      routes:
                        - match:
                            prefix: "/"
                          route:
                            cluster: stepfun
                            timeout: 300s
                http_filters:
                  - name: wasmtest
                    typed_config:
                      "@type": type.googleapis.com/udpa.type.v1.TypedStruct
                      type_url: type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm
                      value:
                        config:
                          name: wasmtest
                          vm_config:
                            runtime: envoy.wasm.runtime.v8
                            code:
                              local:
                                filename: /etc/envoy/plugin.wasm
                          configuration:
                            "@type": "type.googleapis.com/google.protobuf.StringValue"
                            value: |
                              {
                                "provider": {
                                  "type": "stepfun",
                                  "domain": "api.stepfun.com",
                                  "apiTokens": [
                                    "api_token"
                                  ]
                                }
                              }
                  - name: envoy.filters.http.router
  clusters:
    - name: httpbin
      connect_timeout: 30s
      type: LOGICAL_DNS
      # Comment out the following line to test on v6 networks
      dns_lookup_family: V4_ONLY
      lb_policy: ROUND_ROBIN
      load_assignment:
        cluster_name: httpbin
        endpoints:
          - lb_endpoints:
              - endpoint:
                  address:
                    socket_address:
                      address: httpbin
                      port_value: 80
    - name: stepfun
      connect_timeout: 30s
      type: LOGICAL_DNS
      dns_lookup_family: V4_ONLY
      lb_policy: ROUND_ROBIN
      load_assignment:
        cluster_name: stepfun
        endpoints:
          - lb_endpoints:
              - endpoint:
                  address:
                    socket_address:
                      address: api.stepfun.com
                      port_value: 443
      transport_socket:
        name: envoy.transport_sockets.tls
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.transport_sockets.tls.v3.UpstreamTlsContext
          "sni": "api.stepfun.com"

Request:

curl "http://localhost:10000/v1/chat/completions"  -H "Content-Type: application/json" -d '{
"model": "step-1-8k",
"messages": [
    {
        "role": "system",
        "content": "你是由阶跃星辰提供的AI聊天助手，你擅长中文，英文，以及多种其他语言的对话。在保证用户数据安全的前提下，你能对用户的问题和请求，作出快速和精准 的回答。同时，你的回答和建议应该拒绝黄赌毒，暴力恐怖主义的内容。"
    },
    {
        "role": "user",
        "content": "你好，请介绍一下阶跃星辰的人工智能！"
    }
]
}'

Response

{
  "id": "c0ab86c4213e81665861b1ef792377ef.018fc2def96479d5ab2211389dc00bbc",
  "object": "chat.completion",
  "created": 1716961343,
  "model": "step-1-8k",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "阶跃星辰是一家致力于提供人工智能技术的公司。他们的人工智能技术旨在为用户提供高效、精准的回答和建议。这种技术可以理解和处理多种语言，包括中文、英文以及其他一些语言。\n\n阶跃星辰的AI聊天助手能够快速理解用户的问题和请求，并提供相关的回答。它还能够保护用户的数据安全，确保用户的个人信息得到妥善处理。此外，这个AI聊天助手还能够拒绝黄赌毒、暴力恐怖主义等不良内容，为用户提供一个健康、积极的交流环境。\n\n总之，阶跃星辰的人工智能技术旨在为用户提供更好的交流体验，帮助他们解决问题、获取信息，并在这个过程中保护他们的数据安全。"
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 85,
    "completion_tokens": 141,
    "total_tokens": 226
  }
}

Ⅴ. Special notes for reviews

[CH3CHO]

LGTM. Thanks.

[johnlanni]

@Chi-Kai Please resolve the conflicts