feat: add OpenAI-compatible AI provider plugin with SSE streaming support

- Implemented the OpenAI-compatible AI provider plugin, including configuration, chat, and chat_stream functionalities.
- Added support for SSE streaming and tool calls.
- Integrated Boost.JSON for JSON handling.
- Created CMake configuration for the plugin.
- Added error handling and logging throughout the plugin.

plugins_upper/CMakeLists.txt

@@ -0,0 +1,7 @@
+# ============================================================
+# 依赖其他插件的插件 / Plugins depending on non-base plugins
+# ============================================================
+
+add_subdirectory(context)      # 依赖 session / depends on session
+add_subdirectory(openai)       # 依赖 http, config / depends on http, config
+add_subdirectory(anthropic)    # 依赖 http, config / depends on http, config