This adds a flag loaded from the registration file of an AS that will determine whether or not its users are rate limited (by ratelimit in _base.py). Needed for IRC bridge reasons - see https://github.com/matrix-org/matrix-appservice-irc/issues/240.
If 'url' is not specified, they will not be pushed for events or queries. This
is useful for bots who simply wish to reserve large chunks of user/alias
namespace, and don't care about being pushed for events.
SYN-287
This requires that HS owners either opt in or out of stats reporting.
When --generate-config is passed, --report-stats must be specified
If an already-generated config is used, and doesn't have the
report_stats key, it is requested to be set.
