Actually pass ssh/config through to SSHKit options

This option is documented as available since basecamp#908 in:
https://github.com/basecamp/kamal/blob/74a06b0ccda616c86ebe1729d0795f39bcac9f00/lib/kamal/configuration/docs/ssh.yml#L65-L70

However, before this the options don't seem to pass through to SSHKit:
https://github.com/basecamp/kamal/blob/74a06b0ccda616c86ebe1729d0795f39bcac9f00/lib/kamal/commander.rb#L167

Since `config` isn't actually return in this hash.

lib/kamal/configuration/ssh.rb

@@ -38,8 +38,12 @@ def key_data
     ssh_config["key_data"]
   end
 
+  def config
+    ssh_config["config"]
+  end
+
   def options
-    { user: user, port: port, proxy: proxy, logger: logger, keepalive: true, keepalive_interval: 30, keys_only: keys_only, keys: keys, key_data: key_data }.compact
+    { user: user, port: port, proxy: proxy, logger: logger, keepalive: true, keepalive_interval: 30, keys_only: keys_only, keys: keys, key_data: key_data, config: config }.compact
   end
 
   def to_h