Update DID methods list to allow multiple registrations per resolution

[wip-abramson]

RESOLUTION: Allow multiple registrations in the DID Methods extensions list but make it clear in the registration process that doing so is potentially problematic (due to interop concerns). Duplicates will have an issue raised to track the concern and noted in the list, with the registrants asked to address the concern. Duplicate registrations will be listed in chronological order by date of initial listing.

https://www.w3.org/2024/12/19-did-minutes.html#e64a