Improve the Digital Identity Anchor (DIA) definition in the Glossary

The current (as of 16 April) definition for the Digital Identity Anchor (DIA) in the glossary is:

A Digital Identity Anchor (DIA) is a specialized Verifiable Credential, issued by an Authoritative Registrar, that serves as a secure digital attestation anchoring a legally recognized identifier and subject to an entity-controlled Decentralized Identifier (DID). The DIA acts as a "trust wrapper" or digital envelope that provides functional equivalence to traditional registry extracts within digital-first environments. The DIA is not a novel identifier and does not supersede existing legal statuses.

(see https://un.opensource.unicc.org/unece/uncefact/gtr/docs/Documents/Glossary, and source here: https://opensource.unicc.org/un/unece/uncefact/gtr/-/blob/main/docs/Documents/01_Glossary.md

It was agreed at the 2 April meeting that this definition could and should be improved.