Feat: Support tool calling in Generate component (#7572)

### What problem does this PR solve?

Hello, our use case requires LLM agent to invoke some tools, so I made a
simple implementation here.

This PR does two things:

1. A simple plugin mechanism based on `pluginlib`:

This mechanism lives in the `plugin` directory. It will only load
plugins from `plugin/embedded_plugins` for now.

A sample plugin `bad_calculator.py` is placed in
`plugin/embedded_plugins/llm_tools`, it accepts two numbers `a` and `b`,
then give a wrong result `a + b + 100`.

In the future, it can load plugins from external location with little
code change.

Plugins are divided into different types. The only plugin type supported
in this PR is `llm_tools`, which must implement the `LLMToolPlugin`
class in the `plugin/llm_tool_plugin.py`.
More plugin types can be added in the future.

2. A tool selector in the `Generate` component:

Added a tool selector to select one or more tools for LLM:


![image](https://github.com/user-attachments/assets/74a21fdf-9333-4175-991b-43df6524c5dc)

And with the `bad_calculator` tool, it results this with the `qwen-max`
model:


![image](https://github.com/user-attachments/assets/93aff9c4-8550-414a-90a2-1a15a5249d94)


### Type of change

- [ ] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):

Co-authored-by: Yingfeng <yingfeng.zhang@gmail.com>

plugin/plugin_manager.py

@@ -0,0 +1,45 @@
+import logging
+import os
+from pathlib import Path
+import pluginlib
+
+from .common import PLUGIN_TYPE_LLM_TOOLS
+
+from .llm_tool_plugin import LLMToolPlugin
+
+
+class PluginManager:
+    _llm_tool_plugins: dict[str, LLMToolPlugin]
+
+    def __init__(self) -> None:
+        self._llm_tool_plugins = {}
+
+    def load_plugins(self) -> None:
+        loader = pluginlib.PluginLoader(
+            paths=[str(Path(os.path.dirname(__file__), "embedded_plugins"))]
+        )
+        
+        for type, plugins in loader.plugins.items():
+            for name, plugin in plugins.items():
+                logging.info(f"Loaded {type} plugin {name} version {plugin.version}")
+
+                if type == PLUGIN_TYPE_LLM_TOOLS:
+                    metadata = plugin.get_metadata()
+                    self._llm_tool_plugins[metadata["name"]] = plugin
+
+    def get_llm_tools(self) -> list[LLMToolPlugin]:
+        return list(self._llm_tool_plugins.values())
+
+    def get_llm_tool_by_name(self, name: str) -> LLMToolPlugin | None:
+        return self._llm_tool_plugins.get(name)
+
+    def get_llm_tools_by_names(self, tool_names: list[str]) -> list[LLMToolPlugin]:
+        results = []
+
+        for name in tool_names:
+            plugin = self._llm_tool_plugins.get(name)
+
+            if plugin is not None:
+                results.append(plugin)
+
+        return results