Document in detail the `group` functionality feature

As a
Subject Matter Expert (SME) familiar with the implementation and design rationale of the `group` functionality/feature in Casper,

I want to
provide detailed technical, input—including explanations, the user-land access control, use cases, examples, and known limitations—

So that
the documentation team can create a well-structured, developer-focused guide that enables smart contract developers to effectively understand, implement, and evaluate the use of groups in access control.