Split lock and connection setup

Allow run the pre-connect hook before the first SSH command is executed,
but only run the locking in `with_lock` blocks.

lib/kamal/commander.rb

@@ -2,12 +2,13 @@ require "active_support/core_ext/enumerable"
 require "active_support/core_ext/module/delegation"
 
 class Kamal::Commander
-  attr_accessor :verbosity, :holding_lock
+  attr_accessor :verbosity, :holding_lock, :connected
   delegate :hosts, :roles, :primary_host, :primary_role, :roles_on, :traefik_hosts, :accessory_hosts, to: :specifics
 
   def initialize
     self.verbosity = :info
     self.holding_lock = false
+    self.connected = false
     @specifics = nil
   end
 
@@ -137,6 +138,10 @@ class Kamal::Commander
     self.holding_lock
   end
 
+  def connected?
+    self.connected
+  end
+
   private
     # Lazy setup of SSHKit
     def configure_sshkit_with(config)