feat: add free tier Stripe subscription

packages/ee/server-only/stripe/get-customer.ts

@@ -0,0 +1,19 @@
+import { stripe } from '@documenso/lib/server-only/stripe';
+
+export const getStripeCustomerByEmail = async (email: string) => {
+  const foundStripeCustomers = await stripe.customers.list({
+    email,
+  });
+
+  return foundStripeCustomers.data[0] ?? null;
+};
+
+export const getStripeCustomerById = async (stripeCustomerId: string) => {
+  try {
+    const stripeCustomer = await stripe.customers.retrieve(stripeCustomerId);
+
+    return !stripeCustomer.deleted ? stripeCustomer : null;
+  } catch {
+    return null;
+  }
+};