Merge branch 'msj-focus-mode-docs' into 'master'

Add link to version history

See merge request gitlab-org/gitlab!28931

doc/user/project/issue_board.md

@@ -206,7 +206,7 @@ If you don't have editing permission in a board, you're still able to see the co
 ### Focus mode
 
 > - Introduced in [GitLab Starter 9.1](https://about.gitlab.com/releases/2017/04/22/gitlab-9-1-released/#issue-boards-focus-mode-ees-eep).
-> - Focus mode moved to GitLab Core in GitLab 12.10.
+> - [Moved](https://gitlab.com/gitlab-org/gitlab/-/issues/212331) to GitLab Core in 12.10.
 
 Click the button at the top right to toggle focus mode on and off. In focus mode, the navigation UI is hidden, allowing you to focus on issues in the board.