feat(slack): update reaction emoji on task completion

Remove the in-progress reaction (reactEmoji) and optionally add a
done reaction (doneEmoji) when the final response is sent, so users
get visual feedback that processing has finished.

Signed-off-by: Sihyeon Jang <sihyeon.jang@navercorp.com>

nanobot/config/schema.py

@@ -13,7 +13,6 @@ class Base(BaseModel):
 
     model_config = ConfigDict(alias_generator=to_camel, populate_by_name=True)
 
-
 class ChannelsConfig(Base):
     """Configuration for chat channels.