add support for progressive loading and hydration strategies

[thescientist13]

Currently there is no specific strategy for loading any JavaScript rendered with WCC. WCC can / should be able to forward attributes as hints in metadata, so would like to support

1. no JS / SSG (default)
2. eager loading - loading="eager"
3. lazy - loading="lazy"
4. progressive - TBD (scroll, click, etc)

For JavaScript that is needed, should try and programmatically addPassthroughCopy for the user.

Might need some help from WCC for no. 3.