feat(langchain): document interrupts in middleware

[christian-bromann]

We received the following feedback from @casparb

There should be mention in the middleware docs of which middleware you can and cannot raise interrupts in. E.g. I've seen a few cases where people reading the docs think it makes sense to raise an interrupt in @wrap_tool_call to validate a tool message before it's sent to the model. But you can't raise an interrupt here, because on resume you'd re-execute ToolNode.
Maybe more generally HITL middleware should be expanded to have an interrupt_after param. I don't really know what the alternative to this looks like? look at the last message in the messages list and inspect the tool call name in a before_model middleware?

This patch adds a section speaking about how to use interrupts in middleware.

[github-actions]

Mintlify preview ID generated: preview-cbinte-1762814329-ae78f42