Docs: Add more details about possible values for block assets in block.json

[gziolo]

What?

Follow-up for #44155.

It tries to address the comment left by @ryanwelcher in #44155 (comment):

These are confusing for me. Can we use an array of file:./ references here or do the scripts/styles have to be registered elsewhere? I think we need to add some text somewhere that explains this.

How?

It adds similar messages that elaborate on what values can be passed with reference to the section that takes a deeper dive.

[gziolo]

There is an article from explaining how to define styles, scripts, and other fields in block.json:

https://www.billerickson.net/building-acf-blocks-with-block-json/

It’s primarily for ACF Blocks plugin, but there is a lot of overlap.