Merge branch 'feat/manual-variables-tab-frontend-part-one' into 'master'

Feat: manual variables tab frontend part one

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/159206



Merged-by: Vitaly Slobodin <vslobodin@gitlab.com>
Approved-by: Ottilia Westerlund <12746880-ottilia_westerlund@users.noreply.gitlab.com>
Approved-by: Briley Sandlin <bsandlin@gitlab.com>
Approved-by: Vitaly Slobodin <vslobodin@gitlab.com>
Reviewed-by: Ezekiel Kigbo <3397881-ekigbo@users.noreply.gitlab.com>
Reviewed-by: Wu Jeremy <8749551-JeremyWuuuuu@users.noreply.gitlab.com>
Co-authored-by: JeremyWuuuuu <jeremyw@jihulab.com>