Merge branch 'russell/add-iteration-filtering-option' into 'master'

Added iteration to list of filter options

See merge request gitlab-org/gitlab!48348

doc/user/project/issue_board.md

@@ -446,6 +446,7 @@ the list by filtering by the following:
 - Assignee
 - Author
 - Epic
+- Iteration ([introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/118742) in GitLab 13.6)
 - Label
 - Milestone
 - My Reaction
@@ -473,6 +474,7 @@ You can filter by the following:
 - Assignee
 - Author
 - Epic
+- Iteration ([introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/118742) in GitLab 13.6)
 - Label
 - Milestone
 - My Reaction