Better "AI" output in Slack

[StefMa]

Right now we just send back the information we received back to the thread as soon as we have them.
I thought we can do this a little bit better by sending first 🧠 Thinking 🧠 as a message.

We will then replace that message with either
💀 Braindead 💀. Something went wrong. Please try again.`
on failure or with the actual message on success.

In any case, we should also add somekind of "header" like we in the action:

This is a AI generated summarization of this thread. Powered by [summaraizer](https://github.com/ioki-mobility/summaraizer) via [summaraizer-slack](https://github.com/ioki-mobility/summaraizer-slack):</br></br> $body

To indicate that this message was coming from this bot and is AI generated.