Merge branch '372889-bubbis-md-auto-numbering' into 'master'

Automatically update subsequent ordered lines in plain markdown editor

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/179924



Merged-by: Himanshu Kapoor <hkapoor@gitlab.com>
Approved-by: Sascha Eggenberger <seggenberger@gitlab.com>
Approved-by: Diana Zubova <dzubova@gitlab.com>
Approved-by: Himanshu Kapoor <hkapoor@gitlab.com>
Reviewed-by: Diana Zubova <dzubova@gitlab.com>
Reviewed-by: Sascha Eggenberger <seggenberger@gitlab.com>
Co-authored-by: Samuel Suikkanen <samuel.suikkanen@hotmail.com>