refactor: Set user agent for API calls in base settings

The code changes in `base.py` add a `user_agent` attribute to the `Settings` class and a corresponding class method `set_user_agent` to set the user agent for API calls. If the `user_agent` is not provided, it defaults to "langflow". The method also updates the `USER_AGENT` environment variable and logs the new value. This refactor improves the flexibility and maintainability of the code. The commit message follows the established convention of using a prefix to indicate the type of change.

src/backend/base/langflow/services/settings/base.py

@@ -119,8 +119,22 @@ class Settings(BaseSettings):
     """Timeout for the API calls in seconds."""
     frontend_timeout: int = 0
     """Timeout for the frontend API calls in seconds."""
+    user_agent: str = "langflow"
+    """User agent for the API calls."""
+
+    @field_validator("user_agent", mode="after")
+    @classmethod
+    def set_user_agent(cls, value):
+        if not value:
+            value = "langflow"
+        import os
+
+        os.environ["USER_AGENT"] = value
+        logger.debug(f"Setting user agent to {value}")
+        return value
 
     @field_validator("config_dir", mode="before")
+    @classmethod
     def set_langflow_dir(cls, value):
         if not value:
             from platformdirs import user_cache_dir
@@ -144,6 +158,7 @@ class Settings(BaseSettings):
         return str(value)
 
     @field_validator("database_url", mode="before")
+    @classmethod
     def set_database_url(cls, value, info):
         if not value:
             logger.debug("No database_url provided, trying LANGFLOW_DATABASE_URL env variable")