Allow background prop on `Container`

[GuillaumeRx]

We should make the background configurable for Container to allow Snaps to choose between white and gray background. There may be places where we want to not honor this background choice, e.g. insights.

[ajeetd]

Support for this should be for: Pre-installed Snaps && hideSnapsBranding

Do a review of how components look on white background.

[ajeetd]

Confirmations background for Bitcoin/Solana?

[ajeetd]

Implement and fix PoC as needed.

[ajeetd]

Erik following up with DS on additional color.