Merge branch 'document-decision-about-stages-strategy-in-custom-ci-blueprint' into 'master'

Document pipeline execution stages strategy

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143345



Merged-by: Andy Soiron <asoiron@gitlab.com>
Reviewed-by: Furkan Ayhan <furkanayhn@gmail.com>
Reviewed-by: Fabio Pitino <fpitino@gitlab.com>