Merge branch '521595-add-migration-reindex-task-helper' into 'master'

Add Elasticsearch migration reindex task helper

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/183499



Merged-by: Madelein van Niekerk <mvanniekerk@gitlab.com>
Approved-by: Madelein van Niekerk <mvanniekerk@gitlab.com>
Approved-by: Ravi Kumar <rkumar@gitlab.com>
Reviewed-by: Madelein van Niekerk <mvanniekerk@gitlab.com>
Co-authored-by: Arturo Herrero <arturo.herrero@gmail.com>