Feature: Gradient BG support

[Salman2301]

Add a support for linear gradient

• Add a new column for type of background solid | linear-gradient | ...
• For now UI,
  • Select dropdown, to select type of background default to solid
  • on Linear Gradient, Show two color input box
  • Angle of input, valid from 0 to 359°

[cmgriffing]

I think we end up needing more columns in the db.

For now, I think we need:

• bgType: "solid" | "linearGradient"
• bgGradientColorStart: string
• bgGradientColorEnd: string
• bgGradientLinearDirection: number (0 - 359)

So making sure we have those in the validation might be good too.