[Improvement] Map usernames before sending to OpenAI

[yGuy]

For some features (summarization, e.g.) we transmit the user names to OpenAI, but there are very strict limits about the user names in place at OpenAI.

We should rather come up with unique dummy user names that adhere to the strict limits and send them to OpenAI, instead. When the response comes back we should search and replace the dummy names with the real names again. This would allow having arbitrary user names and also adds a little bit of privacy.