Adjust the subject display in dashboard mode to ensure GDPR compliance on public office screens

[muellerp11811]

Description

• The dashboard is used on large public office screens where issue subjects may be visible to people who are not directly involved in the corresponding ticket.
• To reduce the risk of exposing personal or sensitive information, dashboard mode should support displaying an alternative subject instead of the original issue subject.

Proposed change

• Introduce a new dashboard issue view mode called wallboard.
• This mode should:
  * be based on the existing compact view
  • display the issue start_date
  • display a custom issue field named wallboard-subject instead of the original issue subject when the custom field is filled
  • fall back to the original issue subject if wallboard-subject is empty

Motivation

• Issue subjects may contain personal data or confidential information that should not be shown on shared or publicly visible screens.
• The new wallboard mode allows teams to provide a sanitized display text for office dashboards while keeping the original issue subject unchanged in the ticket itself.

Implementation notes

• add wallboard as a new issue view mode
• create a dedicated _wallboard.html.slim partial
• add locale entries for the new view mode
• add an IssueCustomField named wallboard-subject
• use the custom field value in wallboard mode if present

Expected result

• Teams can use dashboard screens in shared office environments without exposing full ticket subjects, helping to support GDPR-conscious operation.