PPP IPCP Extensions for Encrypted DNS Server Negotiation

This document defines extensions to the Point-to-Point Protocol (PPP) Internet Protocol Control Protocol (IPCP) for negotiating encrypted DNS resolver configurations. These extensions allow PPP peers to exchange information about encrypted DNS servers supporting protocols such as DNS over TLS (DoT), DNS over HTTPS (DoH), and DNS over QUIC (DoQ). The design maintains backward compatibility with RFC 1877 while addressing modern security requirements.