BREAKING CHANGE: Remove custom transport support, use Payload's email config

- Removed custom transport configuration from plugin
- Plugin now requires Payload email to be configured
- Simplified setup by relying on Payload's email adapter
- Updated README with new configuration requirements
- Bump version to 0.2.0 (breaking change)

Users must now configure email in their Payload config using an email adapter
like @payloadcms/email-nodemailer instead of configuring transport in the plugin.

dev/payload.config.ts

@@ -135,15 +135,6 @@ const buildConfigWithMemoryDB = async () => {
       mailingPlugin({
         defaultFrom: 'noreply@test.com',
         initOrder: 'after',
-        transport: {
-          host: 'localhost',
-          port: 1025, // MailHog port for dev
-          secure: false,
-          auth: {
-            user: 'test',
-            pass: 'test',
-          },
-        },
         retryAttempts: 3,
         retryDelay: 60000, // 1 minute for dev
         queue: 'email-queue',