fix(GlDuoChat): multi-line prompt support

mentioned in commit ad4c3e41

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!227 (merged)

mentioned in merge request status-page!883 (merged)

mentioned in merge request gitlab!135597 (merged)

mentioned in merge request gitlab!135848 (merged)

mentioned in merge request gitlab-docs!4372 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3598 (merged)

mentioned in merge request status-page!886 (merged)

mentioned in merge request status-page!888 (merged)