Support "encoding", which is required by PHPMailerLite, in SES adapter

Summary: See <https://discourse.phabricator-community.org/t/amazon-ses-adapator-broken-after-upgrade/1121>. The adapter class tree is a mess and this property is read by the parent class.

Test Plan: Configured an SES mailer, used `bin/mail send-test` to reproduce the issue before the patch and observe it working after the patch.

Differential Revision: https://secure.phabricator.com/D19083

src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php

@@ -26,6 +26,7 @@ final class PhabricatorMailImplementationAmazonSESAdapter
         'access-key' => 'string',
         'secret-key' => 'string',
         'endpoint' => 'string',
+        'encoding' => 'string',
       ));
   }
 
@@ -34,6 +35,7 @@ final class PhabricatorMailImplementationAmazonSESAdapter
       'access-key' => null,
       'secret-key' => null,
       'endpoint' => null,
+      'encoding' => 'base64',
     );
   }
 
@@ -42,6 +44,7 @@ final class PhabricatorMailImplementationAmazonSESAdapter
       'access-key' => PhabricatorEnv::getEnvConfig('amazon-ses.access-key'),
       'secret-key' => PhabricatorEnv::getEnvConfig('amazon-ses.secret-key'),
       'endpoint' => PhabricatorEnv::getEnvConfig('amazon-ses.endpoint'),
+      'encoding' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-encoding'),
     );
   }