Icon support for SettingButton and SettingPicker and trailing label support for SettingPage

[Saik0s]

Thanks for creating an awesome library!

This PR implements icon support for SettingButton and SettingPicker, as well as trailing label support for SettingPage, to ensure consistency with the look and feel of iOS Settings.

[Saik0s]

This PR would cover #12

[aheze]

Thanks for the PR - sorry for getting back to you so late. Checking this out...

[aheze]

Thanks!

[aheze]

Resolved the merge conflict here: 4f9c736

[aheze]

Added an example:

SettingPage(title: "Extras", selectedChoice: "Hello, world!") {
    SettingGroup {
        SettingButton(title: "Hello, world!") {
            print("Hello world pressed!")
        }
        .icon(icon: .system(icon: "ellipsis", backgroundColor: Color.teal))
    }
    
    SettingGroup {
        SettingButton(title: ":)") {
            print(":) pressed!")
        }
        .icon(icon: .system(icon: "sparkles", backgroundColor: Color.pink))
        .indicator("face.smiling")
    }
}
.previewIcon(icon: .system(icon: "ellipsis", backgroundColor: Color.teal))