Add a sample snapshot test for a SwiftUI View

[pinarol]

Closes part of #539

Description

Adds a snapshot test for AvatarPickerProfileView to demonstrate how we can do snapshot testing for SwiftUI Views.

Uses Snapshotting.image(...) strategy from the existing snapshot library. It is a snapshot strategy for comparing SwiftUI Views based on pixel equality. There are different layout types we can pass, but .sizeThatFits didn't work well for this view not sure why. So I just used .device and put some red borders around the content so the bounds are also visible and comparable.

Testing Steps

CI green.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Gravatar Prototype Build by scanning the QR code below to install the corresponding build.

	App Name	Gravatar Prototype Build
	Build Number	1897
	Version	1.0
	Bundle ID	com.automattic.gravatar-sdk-demo-uikit.prototype-build
	Commit	b8ed089
	App Center Build	Gravatar SDK Demo - UIKit #482

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[etoledom]

Just a question:
Is there a way to snapshot only de view without the whole bound of the device screen?

[pinarol]

Can you check again? @etoledom I think I found a way to make .sizeThatFits work by applying a custom .frame(...)

[etoledom]

Looks great 👍