SA: Use IgnoreAccountContacts flag to shortcut UpdateRegistrationContact (#8208)

If the IgnoreAccountContacts flag is set, don't bother writing the new
contacts to the database and instead just return the account object as
it stands. This does not require any test changes because
#8198 already changed
registrationModelToPb to omit whatever contacts were retrieved from the
database before responding to the RA.

Part of #8176

Author: aarongable

sa/sa.go

@@ -21,6 +21,7 @@ import (
 	corepb "github.com/letsencrypt/boulder/core/proto"
 	"github.com/letsencrypt/boulder/db"
 	berrors "github.com/letsencrypt/boulder/errors"
+	"github.com/letsencrypt/boulder/features"
 	bgrpc "github.com/letsencrypt/boulder/grpc"
 	"github.com/letsencrypt/boulder/identifier"
 	blog "github.com/letsencrypt/boulder/log"
@@ -132,6 +133,10 @@ func (ssa *SQLStorageAuthority) UpdateRegistrationContact(ctx context.Context, r
 		return nil, errIncompleteRequest
 	}
 
+	if features.Get().IgnoreAccountContacts {
+		return ssa.GetRegistration(ctx, &sapb.RegistrationID{Id: req.RegistrationID})
+	}
+
 	// We don't want to write literal JSON "null" strings into the database if the
 	// list of contact addresses is empty. Replace any possibly-`nil` slice with
 	// an empty JSON array.