Allow bots to get activity metadata

[Cynosphere]

Bots cannot currently use the application metadata endpoint (/users/:id/sessions/:session_id/activities/:application_id), which the only usage currently is for button URLs. It would be nice to have a way for bots to get button URLs for commands that list presences or even moderation since the client does not currently have a way to show where the button takes you and reuses the same link opening logic as messages, meaning that invites are accepted with no confirmation.

Presences are already a privileged intent as is, so there shouldn't be privacy concerns in allowing this.