AlternatedBackground doesn't work with custom top margin

[johnferchermeli]

Describe the bug
When defined a custom top page margin, the alternated background doesn't consider the new value in the y offset and doesn't fill the background correctly. This is a limitation from CellFormat.

Related code:

m := pdf.NewMaroto(consts.Portrait, consts.A4)
m.SetPageMargins(10, 15, 10)

m.TableList(headerSmall, smallContent, props.TableList{
	AlternatedBackground: &color.Color{
		Red:   200,
		Green: 200,
		Blue:  200,
	},
})

Expected behavior

• The alternated background should fill the background correctly, considering the new top margin.