[Feature]: Add verification method for companion ownership via bot-generated message

[MrAlders0n]

Platform: Other

Description:
Would love aswell an additional way to show ownership of a companion like being asked to send a message that Meshmapper has generated with example /verify hCevIM in a bot specific chat so an observer reporting to Meshmapper could confirm it is from the right public key. 🤗

Discord: https://discord.com/channels/1463383723327356992/1466576054670987294/1522500399016444017

Submitted by: jesper02 (Discord)