Add a field to allow identity claims aggregator to describe how a verification was performed

[scouten-adobe]

Follow up to 03 December 2024 CAWG meeting.

Per @christianpaquin , this is a blocker for 1.1 ratification.

[christianpaquin]

To expand of what I said: having the aggregator simply state something like "I verified the actor's website" seems incomplete, and something like "I verified the actor's website using <method>", where <method> is an existing website validation procedure such as:

• DNS verification (like this one)
• File based validation (like this one)
• Email-based validation (like this one)
• Meta-tag validation (like this one)
• Social platform's OAuth api

An optional field with some of these predefined options would do.