Consider adding ed25519 identities to fallback list

The fallback list is in the format:

"185.220.100.255 orport=9100 id=7327876AE79C997DFE311A7B15B4FA875736BBD1"
" ipv6=[2a0b:f4c0:16c:1::1]:9100"
/* nickname=F3Netze */
/* extrainfo=0 */
/* ===== */
,

The id here is just the legacy fingerprint. This means that new clients will connect to relays using only the legacy identity.

As long as clients only use these fallback entries as the first hop and don't extend circuits to these entries, then I think this shouldn't affect the future arti-relay change of "don't allow EXTEND2 messages with only the rsa identity link specifier".

But it might still be good to update this as part of the "migrate towards using Ed25519 everywhere" plan.