Multi-select for projects dropdown filter
What does this MR do?
This MR adds the multi-select option to the projects dropdown filter which is used for group cycle / productivity analytics
Does this MR meet the acceptance criteria?
Conformity
Part of https://gitlab.com/gitlab-org/gitlab-ee/issues/12078 https://gitlab.com/gitlab-org/gitlab-ee/issues/12753
Follow up MR from https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14595
Edited by Brandon Labuschagne