Is your feature request related to a problem? Please describe.
Right now we're limited to either implement tool calling within a function/pipeline directly, or using the default function calling pipeline.

• By re-implementing tool calling in a pipeline, we have to define all tools directly, which makes it harder for users to pull extra tools. Additionally, we can't select/de-select them from the UI.
• By using native tool calling, we can't control when tools are called (for example, it's impossible to implement an OpenAI-like tool call in the middle of a message), and in the case of functions, we can't know when the pipe() function is called to generate tool call responses.

Describe the solution you'd like
For a function/pipeline, add an optional attribute called "prepend_tools" that decides if the tools are called and appended to the system prompt before responding.
Add an optional parameter to pipe(), called, say, __tool_signatures__ and __tool_callables__ (or simply __tools__: dict) with __tools__["signatures"] and __tools__["callables"] pointing to signatures (in OpenAI JSON format) and and callables respectively