Add page numbers to header

Currently, a developer can easily add page numbers to a ddk.Page with the ddk.PageFooter. This functionality should be included in the ddk.PageHeader for clients that need that functionality. ## Why is this feature important? With manipulating a single property in the ddk.PageFooter component, developers can add page numbers to the footer of their PDF reports. This is not the case with the ddk.PageHeader, requiring developers to find a dynamic way to add these page numbers making the development more cumbersome.

https://github.com/orgs/plotly/projects/90/views/1?pane=issue&itemId=47500064