Merge branch '462378-allow-more-than-3-additional-properties-in-internal-events-2' into 'master'

Add documentation related to additional properties in Internal Events

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/160567



Merged-by: Ankit Panchal <apanchal@gitlab.com>
Approved-by: Sarah Yasonik <syasonik@gitlab.com>
Approved-by: Ankit Panchal <apanchal@gitlab.com>
Reviewed-by: Sarah Yasonik <syasonik@gitlab.com>
Reviewed-by: Ankit Panchal <apanchal@gitlab.com>
Co-authored-by: Niko Belokolodov <nbelokolodov@gitlab.com>