Add missing Issues pages to global nav

Add these pages:

• https://docs.gitlab.com/ee/user/project/issues/associate_zoom_meeting.html
• https://docs.gitlab.com/ee/user/project/issues/crosslinking_issues.html
• https://docs.gitlab.com/ee/user/project/issues/issue_data_and_actions.html
• https://docs.gitlab.com/ee/user/project/issues/managing_issues.html
• https://docs.gitlab.com/ee/user/project/issues/multiple_assignees_for_issues.html
• https://docs.gitlab.com/ee/user/project/issues/sorting_issue_lists.html
• https://docs.gitlab.com/ee/user/project/milestones/burndown_charts.html moved to gitlab-docs#810 (closed)