Set and remember a URL for that game/channel's character keeper

[junbl]

Add a command that allows non-privileged users to add links to their character sheet to a pinned post on a given channel.

Think this should just make a pinned post with a predefined structure, like

# GAME LINKS
Foundry IP (local) - 192.168.0.1
Foundry IP (remote) - 999.888.777.666
Custom link from the GM - https://some.relevant.website/

## PLAYERS
Chemehevna - https://character.sheet/chemehevna
Dorklebrow - https://...
Benhemmerich - https://...

Not sure if there's a use case where players would need/want to put it custom links per character.