Merge branch '23403-fix-events-for-private-project-features' into 'security'

Respect project visibility settings in the contributions calendar

This MR fixes a number of bugs relating to access controls and date selection of events for the contributions calendar

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/23403



See merge request !2019

Signed-off-by: Rémy Coutable <remy@rymai.me>