chore: Uses pydantic Field for Agent configs, so that the generated AgentConfig.json json schema can carry field description

PiperOrigin-RevId: 797094012

Author: Jacksunwei

src/google/adk/agents/base_agent_config.py

@@ -24,6 +24,7 @@
 
 from pydantic import BaseModel
 from pydantic import ConfigDict
+from pydantic import Field
 
 from ..utils.feature_decorator import experimental
 from .common_configs import AgentRefConfig
@@ -43,32 +44,41 @@ class BaseAgentConfig(BaseModel):
       extra='allow',
   )
 
-  agent_class: Union[Literal['BaseAgent'], str] = 'BaseAgent'
-  """Required. The class of the agent. The value is used to differentiate
-  among different agent classes."""
+  agent_class: Union[Literal['BaseAgent'], str] = Field(
+      default='BaseAgent',
+      description=(
+          'Required. The class of the agent. The value is used to differentiate'
+          ' among different agent classes.'
+      ),
+  )
 
-  name: str
-  """Required. The name of the agent."""
+  name: str = Field(description='Required. The name of the agent.')
 
-  description: str = ''
-  """Optional. The description of the agent."""
+  description: str = Field(
+      default='', description='Optional. The description of the agent.'
+  )
 
-  sub_agents: Optional[List[AgentRefConfig]] = None
-  """Optional. The sub-agents of the agent."""
+  sub_agents: Optional[List[AgentRefConfig]] = Field(
+      default=None, description='Optional. The sub-agents of the agent.'
+  )
 
-  before_agent_callbacks: Optional[List[CodeConfig]] = None
-  """Optional. The before_agent_callbacks of the agent.
+  before_agent_callbacks: Optional[List[CodeConfig]] = Field(
+      default=None,
+      description="""\
+Optional. The before_agent_callbacks of the agent.
 
-  Example:
+Example:
 
-    ```
-    before_agent_callbacks:
-      - name: my_library.security_callbacks.before_agent_callback
-    ```
-  """
+  ```
+  before_agent_callbacks:
+    - name: my_library.security_callbacks.before_agent_callback
+  ```""",
+  )
 
-  after_agent_callbacks: Optional[List[CodeConfig]] = None
-  """Optional. The after_agent_callbacks of the agent."""
+  after_agent_callbacks: Optional[List[CodeConfig]] = Field(
+      default=None,
+      description='Optional. The after_agent_callbacks of the agent.',
+  )
 
   def to_agent_config(
       self, custom_agent_config_cls: Type[TBaseAgentConfig]