Add additional context to AiChat GraphQL mutation

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/161898



Merged-by: Leaminn Ma <lma@gitlab.com>
Approved-by: Shinya Maeda <shinya@gitlab.com>
Reviewed-by: Shinya Maeda <shinya@gitlab.com>
Reviewed-by: Tetiana Chupryna <tchupryna@gitlab.com>
Co-authored-by: Missy Davies <mdavies@gitlab.com>
Co-authored-by: Vitali Tatarintev <vtatarintev@gitlab.com>