Register `mcp-registry-auth` to "Well-Known URIs"

[scottschreckengaust]

Describe the bug
/.well-known/mcp-registry-auth is missing from the "Well-Known URIs" that tracks RFC8615.

To Reproduce
Steps to reproduce the behavior:

1. https://www.iana.org/assignments/well-known-uris/well-known-uris.xhtml
2. Look for mcp-registry-auth entry

Expected behavior
The mcp-registry-auth should be there.

Logs
If applicable, add logs to help explain your problem.
N/A

Additional context
Add any other context about the problem here.

protocol-registries/well-known-uris#68