Create a context for local builds

This ensures we use the docker-container driver and not whatever the
local default is.

lib/kamal/commands/builder/local.rb

@@ -1,8 +1,10 @@
 class Kamal::Commands::Builder::Local < Kamal::Commands::Builder::Base
   def create
+    docker :buildx, :create, "--name", builder_name, "--driver=docker-container"
   end
 
   def remove
+    docker :buildx, :rm, builder_name
   end
 
   def info
@@ -20,6 +22,10 @@ class Kamal::Commands::Builder::Local < Kamal::Commands::Builder::Base
       build_context
   end
 
+  def context_hosts
+    docker :buildx, :inspect, builder_name, "> /dev/null"
+  end
+
   private
     def builder_name
       "kamal-local"