Wait for ratelimits when sending invites (and emit a count of the number of sent invites)

[reivilibre]

Pulled out of FOSDEM 2024 hotfixes #228

I think it's still worth bumping up the rate-limit, but the rate-limit respect is a nice-to-have in the case where you can't easily do that and you have an awkward number of invites to send out.