Organize backend into product executable and shared Go modules

backend/product/verification/config/config.go

@@ -0,0 +1,6 @@
+package config
+
+type Config struct {
+	AllowedPurposes []string                      `yaml:"allowed_purposes"`
+	RateLimits      *VerificationRateLimitsConfig `yaml:"rate_limits"`
+}