Search for issues with multiple assignees

Resources

PM @victorwu | UX @cperessini | FE @alfredo1

Description

With multiple assignees (https://gitlab.com/gitlab-org/gitlab-ce/issues/13386), this is how searching will behave:

I search for: assignee: @victorwu assignee: @ClemMakesApps

I get all issues that are assigned to both @victorwu + @ClemMakesApps. This includes issues that have other assignees. But all the results have at least these two assignees.