Make reserved field configurable

[wen-long]

there is a 3-bytes reserved field in wireguard protocol
some backend (cloudflare warp) use this as client-id, client must configure this field to connect

some wireguard client support this feature, like:
https://sing-box.sagernet.org/configuration/outbound/wireguard/#peers
https://manual.nssurge.com/policy/wireguard.html search client-id

[fscarmen]

Can wireproxy add reseved?

This is an array of 3 numbers.
This way I can use the warp service in LA and HK.