Clearly identify acknowledgements of anonymous contributors via GitHub IDs

[selfissued]

In parallel with the suggestion at w3c/vc-data-model#1585 (comment), acknowledgements of anonymous contributors via their GitHub IDs should be clearly labelled as such, and placed in a separate list from the named contributors.

This should be done across all working group specifications where anonymous contributions are acknowledged via GitHub IDs. I will wait until the working group has discussed this issue before filing similar issues on other specifications affected by this practice.