Add some avatar customization options in ProfileViewConfiguration

[pinarol]

Closes #245

Description

I added following properties to AvatarConfiguration:

• cornerRadiusCalculator: A closure that calculates the corner radius of avatar based on its length.
• borderWidth
• borderColor
• avatarLength

I also removed some logic from DefaultAvatarProvider that waits until the avatar download ends to set the avatar border. I added that logic but I think it wasn't much necessary. I adjusted the placeholder implementation accordingly to hide the border during placeholder state.

Testing Steps

I added snapshot test but I also added a "Customize Avatar" switch to Demo App > Profile View controller. Demo App> Profile Cards can also be checked to see if there are regressions.

[pinarol]

I was curious how/why snapshot of empty views has changed:

The diff is on the border and hardly recognizable, I can't say I make much sense of it 🤔

[etoledom]

I like how the loading placeholders automatically adapt to the new shapes ✨