Add built-in support for lazy image loading

[jaredcwhite]

aka the loading="lazy" attribute

[JuanVqz]

what does this mean? Does somebody only need to add that property to the generated img tag to fill this issue out?

[jaredcwhite]

@JuanVqz Essentially, yes. I'm not sure yet if we enforce it or make it configurable somehow (there could be cases where people choose not to lazy load for whatever reason).