Previously we introduced the concept of a "pending orders per account
ID" rate limit. After struggling with making an implementation of this
rate limit perform well we reevaluated the problem and decided a "new
orders per account per time window" rate limit would be a better fit for
ACMEv2 overall.
This commit introduces the new newOrdersPerAccount rate limit. The RA
now checks this before creating new pending orders in ra.NewOrder. It
does so after order reuse takes place ensuring the rate limit is only
applied in cases when a distinct new pending order row would be created.
To accomplish this a migration for a new orders field (created) and an
index over created and registrationID is added. It would be possible to
use the existing expires field for this like we've done in the past, but that
was primarily to avoid running a migration on a large table in prod. Since
we don't have that problem yet for V2 tables we can Do The Right Thing
and add a column.
For deployability the deprecated pendingOrdersPerAccount code & SA
gRPC bits are left around. A follow-up PR will be needed to remove
those (#3502).
Resolves#3410
f2d3ad6d52