Merge branch '379208-expose-chat-notification-field-placeholders' into 'master'

Expose placeholder data for integration channels

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/102481



Merged-by: Alex Pooley <apooley@gitlab.com>
Approved-by: Bojan Marjanovic <bmarjanovic@gitlab.com>
Approved-by: Alex Pooley <apooley@gitlab.com>
Co-authored-by: Luke Duncalfe <lduncalfe@eml.cc>