Add support for Resend mailer

This update expands the mailer support by adding the Resend mailer as an alternative to NodeMailer and Cloudflare Mailer. After setting the environment variable 'MAILER_PROVIDER' to 'resend', users can utilize the Resend HTTP API for mailing. Necessary instructions and variable settings regarding the usage of Resend mailer have also been added to README.md and related modules.

packages/mailers/src/index.ts

@@ -1,7 +1,7 @@
 import { z } from 'zod';
 
 const MAILER_PROVIDER = z
-  .enum(['nodemailer', 'cloudflare'])
+  .enum(['nodemailer', 'cloudflare', 'resend'])
   .default('nodemailer')
   .parse(process.env.MAILER_PROVIDER);
 
@@ -26,6 +26,12 @@ export async function getMailer() {
       return new CloudflareMailer();
     }
 
+    case 'resend': {
+      const { ResendMailer } = await import('./impl/resend');
+
+      return new ResendMailer();
+    }
+
     default:
       throw new Error(`Invalid mailer: ${MAILER_PROVIDER as string}`);
   }