Fix missing buttons example

[retlehs]

Description

The buttons block is missing an example from the block inserter

The button block has an example, but it isn't used from the inserter

How has this been tested?

I forked and git clone'd the repo, built the plugin locally and loaded on my local dev WP running 5.4.2 and no other plugins, default theme

Screenshots

Before

After

Types of changes

Enhancement: This makes sure that the buttons block preview shows an example

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

[Soean]

The buttons block contains inner blocks of the type core/button. If you want to preview custom buttons, you have to add inner blocks:

	example: {
		innerBlocks: [
			{
				name: 'core/button',
				attributes: {
					className: 'is-style-fill',
					backgroundColor: 'vivid-green-cyan',
					text: __( 'Call to Action' ),
				},
			},
		],
	},

If you want to show the example like in the screenshot, you just need to add an empty object:

	example: {},

[retlehs]

@Soean thank you! i updated this PR to just pass the empty example object and it still produces the same output as you mentioned

please let me know if there's any other changes i should make

[Soean]

I think it's good for the example preview. Thanks for contributing!

[youknowriad]

maybe we can be more creative and use something close to the two or three buttons pattern here.