[Feature] Add tool to convert attachment for an llm.thread to document for vector searching via llm_knowledge module

We have a module named [llm_knowledge](https://github.com/apexive/odoo-llm/tree/16.0/llm_knowledge) which converts odoo's ir.attatchment into embedding chunks(llm.document.chunk).

We require an llm.tool, that can handle uploaded attachments in llm.thread to convert that attachment into an llm.document and process, embed it, maybe.