Additional information to log about the action.
This log can be used in a few ways. First, it can be used to audit what exactly the
LLM predicted to lead to this (tool, tool_input).
Second, it can be used in future iterations to show the LLMs prior thoughts. This is
useful when (tool, tool_input) does not contain full information about the LLM
prediction (for example, any thought before the tool/tool_input).
log: str