New MISP object summariser-output added in MISP

Following the overview of RSS pipeline with MISP and other tooling discussed during the hackathon:

A new object template summariser-output has been created to facilitate the sharing of summaries from AI-based or NLP-based summariser software.

This will be used in with https://github.com/aaronkaplan/openai-cti-summarizer/.

Some of the components will be developed during and after the hackathon.