Merge branch 'jnnkl-refactor-duo-chat-streaming' into 'master'

Refactor DuoChat chunk handling

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/148881



Merged-by: Denys Mishunov <dmishunov@gitlab.com>
Approved-by: Denys Mishunov <dmishunov@gitlab.com>
Co-authored-by: Jannik Lehmann <jlehmann@gitlab.com>