Confirmation pattern - the title should probably be an H1

[joelanman]

On a confirmation page the title is currently and H2 - it should probably be an H1

https://design-system.service.gov.uk/patterns/confirmation-pages/default/index.html

[dashouse]

I think we should certainly make the change so it's an<h1> by default but make it configurable, either to allow for an <h2> if desired or perhaps using the same isPageHeading: true logic as the <legend> and <label>?

For example, I believe DVLA use a confirmation panel with an <h2> because the panel is preceded by the vehicles registration mark as the <h1>

[NickColley]

titleLevel: 2 default (1)?

[kr8n3r]

updated in #439