R1:2e72e9ff31fd

Rate limit outbound requests in Macros

Summary:
Ref T6755. Although we do not return response bodies, it is possible to perform crude portscanning if you can execute a DNS rebinding attack (which, for now, remains theoretical).

Limit users to 60 requests / hour to make it less feasible. This would require ~30 years to portscan all ports on a `/32` netblock.

Users who can guess that services may exist can confirm their existence more quickly than this, but if the attacker already had a very small set of…