Document REACTION_MAX_USER_NUM setting option (#27954) (#27959)

Backport #27954 by @6543

as title

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*Sponsored by Kithara Software GmbH*

Co-authored-by: 6543 <m.huber@kithara.com>

custom/conf/app.example.ini

@@ -1219,6 +1219,9 @@ LEVEL = Info
 ;; For custom reactions, add a tightly cropped square image to public/assets/img/emoji/reaction_name.png
 ;REACTIONS = +1, -1, laugh, hooray, confused, heart, rocket, eyes
 ;;
+;; Change the number of users that are displayed in reactions tooltip (triggered by mouse hover).
+;REACTION_MAX_USER_NUM = 10
+;;
 ;; Additional Emojis not defined in the utf8 standard
 ;; By default we support gitea (:gitea:), to add more copy them to public/assets/img/emoji/emoji_name.png and add it to this config.
 ;; Dont mistake it for Reactions.

docs/content/administration/config-cheat-sheet.en-us.md

@@ -223,6 +223,7 @@ The following configuration set `Content-Type: application/vnd.android.package-a
 - `REACTIONS`: All available reactions users can choose on issues/prs and comments
     Values can be emoji alias (:smile:) or a unicode emoji.
     For custom reactions, add a tightly cropped square image to public/assets/img/emoji/reaction_name.png
+- `REACTION_MAX_USER_NUM`: **10**: Change the number of users that are displayed in reactions tooltip (triggered by mouse hover).
 - `CUSTOM_EMOJIS`: **gitea, codeberg, gitlab, git, github, gogs**: Additional Emojis not defined in the utf8 standard.
     By default, we support Gitea (:gitea:), to add more copy them to public/assets/img/emoji/emoji_name.png and
     add it to this config.