Merge branch 'sx/avoid_nplus1_queries_on_work_item_dates_source' into 'master'

Preload dates_source when the widget is requested

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/167620



Merged-by: Marc Saleiko <msaleiko@gitlab.com>
Approved-by: Alexandru Croitor <acroitor@gitlab.com>
Approved-by: Kassio Borges <kborges@gitlab.com>
Approved-by: Marc Saleiko <msaleiko@gitlab.com>
Reviewed-by: Marc Saleiko <msaleiko@gitlab.com>
Co-authored-by: stefanosxan <sxanthopoulos@gitlab.com>