RA: Update duplicate certificate error URL (#6181)

Resolves #6164

errors/errors.go

@@ -114,6 +114,13 @@ func RateLimitError(msg string, args ...interface{}) error {
 	}
 }
 
+func DuplicateCertificateError(msg string, args ...interface{}) error {
+	return &BoulderError{
+		Type:   RateLimit,
+		Detail: fmt.Sprintf(msg+": see https://letsencrypt.org/docs/duplicate-certificate-limit/", args...),
+	}
+}
+
 func RejectedIdentifierError(msg string, args ...interface{}) error {
 	return New(RejectedIdentifier, msg, args...)
 }

ra/ra.go

@@ -1376,7 +1376,7 @@ func (ra *RegistrationAuthorityImpl) checkCertificatesPerFQDNSetLimit(ctx contex
 	names = core.UniqueLowerNames(names)
 	threshold := limit.GetThreshold(strings.Join(names, ","), regID)
 	if count.Count >= threshold {
-		return berrors.RateLimitError(
+		return berrors.DuplicateCertificateError(
 			"too many certificates (%d) already issued for this exact set of domains in the last %.0f hours: %s",
 			threshold, limit.Window.Duration.Hours(), strings.Join(names, ","),
 		)

ra/ra_test.go

@@ -1246,12 +1246,12 @@ func TestCheckExactCertificateLimit(t *testing.T) {
 		{
 			Name:        "FQDN set issuances equal to limit",
 			Domain:      "equal.example.com",
-			ExpectedErr: fmt.Errorf("too many certificates (3) already issued for this exact set of domains in the last 23 hours: equal.example.com: see https://letsencrypt.org/docs/rate-limits/"),
+			ExpectedErr: fmt.Errorf("too many certificates (3) already issued for this exact set of domains in the last 23 hours: equal.example.com: see https://letsencrypt.org/docs/duplicate-certificate-limit/"),
 		},
 		{
 			Name:        "FQDN set issuances above limit",
 			Domain:      "over.example.com",
-			ExpectedErr: fmt.Errorf("too many certificates (3) already issued for this exact set of domains in the last 23 hours: over.example.com: see https://letsencrypt.org/docs/rate-limits/"),
+			ExpectedErr: fmt.Errorf("too many certificates (3) already issued for this exact set of domains in the last 23 hours: over.example.com: see https://letsencrypt.org/docs/duplicate-certificate-limit/"),
 		},
 	}