Refactor concerns into service layer for welcome controller

What does this MR do and why?

Refactor concerns into service layer for welcome controller

• better organization of code and concerns
• move worker to service layer
• move tracking in show to view layer(no behavior change other than needing view to load)
• add tracking matcher for ease of tracking verification
• see #465532 (closed)

MR acceptance checklist

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Related to #465532 (closed)