feat: Add palette icon to NesIcons

[erickzanardo]

Description

Add a new entry to the NesIcons library: palette.

Use this string for is data 8,8;1,-1;6,0;1,-1;2,0;1,1;2,0;1,1;11,0;1,1;4,0;1,1;11,0;1,1;3,0;1,-1;1,0;1,-1;7,0;2,-1;5,0;1,-1

Requirements

• Add a new entry to the NesIcons class
• Add a new entry in the changelog
• Add a new entry in the widgetbook use case
• Make sure dart format pass in both the root folder and widgetbook folder
• Make sure dart analyze pass in both the root folder and widgetbook folder