fix(usage): add missing error filtering for users/admin

[pinglin]

Because

• The TriggerSingleReporter method was missing the same error filtering logic that exists in NewUsage and StartReporter methods
• When GetUserAdmin fails with "users/admin" error, it should be treated as a debug message rather than an error since only Instill Core CE has the default "admin" user
• Without this filtering, false alarm errors were being logged when the admin user doesn't exist in other Instill editions

This commit

• Adds the same error filtering pattern to TriggerSingleReporter that already exists in NewUsage and StartReporter
• Changes the error handling to check if the error contains "users/admin" and treats it as a debug log instead of an error log
• Ensures consistent error handling across all three methods when dealing with the default admin user lookup
• Prevents false alarm error logs in Instill editions that don't have the default admin user