Allow addition of arbitrary meta-data to discovery via key-value TXT pairs like mDNS

[andrewdavidmackenzie]

Allow the addition of meta-data to discovery via an arbitrary number of key-value TXT pairs like mDNS allows.
Then in the "client" (discoveree) then be able to get the values via key, or iterate through them.

Reference implementations for mDNS:

• https://docs.rs/mdns-sd/latest/mdns_sd/ (called "properties) (https://docs.rs/mdns-sd/latest/mdns_sd/struct.ServiceInfo.html)
• https://docs.rs/edge-mdns/latest/edge_mdns/host/struct.Service.html (called "text_kvs")

[andrewdavidmackenzie]

DUPLICATE

[matheus23]

Duplicate of #3002, specifically