Add Pinned Post ability for forum admin

[NielLiesmons]

Zapstore community npub should be able to pin a post to the top of the forum (for Welcome or whatever else)

[franzaps]

v2 stuff...

[NielLiesmons]

💯 , just listing stuff here to not forget myself.
Annoying that I can't set Priority in GH.

[franzaps]

@NielLiesmons use milestones for setting priority