added a recipe for Symfony mailer

symfony/mailer/4.3/config/packages/mailer.yaml

@@ -0,0 +1,3 @@
+framework:
+    mailer:
+        dsn: '%env(MAILER_DSN)%'

symfony/mailer/4.3/manifest.json

@@ -0,0 +1,8 @@
+{
+    "copy-from-recipe": {
+        "config/": "%CONFIG_DIR%/"
+    },
+    "env": {
+        "#1": "MAILER_DSN=smtp://localhost"
+    }
+}

symfony/mailer/4.3/post-install.txt

@@ -0,0 +1,18 @@
+<bg=blue;fg=white>              </>
+<bg=blue;fg=white> What's next? </>
+<bg=blue;fg=white>              </>
+
+  * You're ready to send emails.
+
+  * If you want to send emails via a supported email provider, install
+    the corresponding bridge.
+    For instance, <info>composer require mailgun-bridge</> for Mailgun.
+
+  * If you want to send emails asynchronously:
+
+    1. Install the messenger component by running <info>composer require messenger</>;
+    2. Add <info>'Symfony\Component\Mailer\Messenger\SendEmailMessage': amqp</> to the
+       <info>config/packages/messenger.yaml</> file under <info>framework.messenger.routing</>
+       and replace <info>amqp</> with your transport name of choice.
+
+  * <fg=blue>Read</> the documentation at <comment>https://symfony.com/doc/master/mailer.html</>