Remove confusing placeholder for JIRA transition_id

app/models/project_services/jira_service.rb

@@ -91,7 +91,7 @@ class JiraService < IssueTrackerService
       { type: 'text', name: 'project_key', placeholder: 'Project Key' },
       { type: 'text', name: 'username', placeholder: '' },
       { type: 'password', name: 'password', placeholder: '' },
-      { type: 'text', name: 'jira_issue_transition_id', placeholder: '2' }
+      { type: 'text', name: 'jira_issue_transition_id', placeholder: '' }
     ]
   end

changelogs/unreleased/28574-jira-trigers.yml

+---
+title: Remove confusing placeholder for JIRA transition_id
+merge_request:
+author:

doc/user/project/integrations/jira.md

@@ -101,7 +101,7 @@ in the table below.
 | `Project key` | The short identifier for your JIRA project, all uppercase, e.g., `PROJ`. |
 | `Username` | The user name created in [configuring JIRA step](#configuring-jira). |
 | `Password` |The password of the user created in [configuring JIRA step](#configuring-jira). |
-| `JIRA issue transition` | This is the ID of a transition that moves issues to a closed state. You can find this number under JIRA workflow administration ([see screenshot](img/jira_workflow_screenshot.png)). |
+| `JIRA issue transition` | This is the ID of a transition that moves issues to a closed state. You can find this number under JIRA workflow administration ([see screenshot](img/jira_workflow_screenshot.png)). **Closing JIRA issues via commits or Merge Requests won't work if you don't set the ID correctly.** |
 After saving the configuration, your GitLab project will be able to interact
 with the linked JIRA project.