Copy env files to remote hosts

Setting env variables in the docker arguments requires having them on
the deploy host.

Instead we'll add two new commands `kamal env push` and
`kamal env delete` which will manage copying the environment as .env
files to the remote host.

Docker will pick up the file with `--env-file <path-to-file>`. Env files
will be stored under `<kamal run directory>/env`.

Running `kamal env push` will create env files for each role and
accessory, and traefik if required.

`kamal envify` has been updated to also push the env files.

By avoiding using `kamal envify` and creating the local and remote
secrets manually, you can now avoid accessing secrets needed
for the docker runtime environment locally. You will still need build
secrets.

One thing to note - the Docker doesn't parse the environment variables
in the env file, one result of this is that you can't specify multi-line
values - see https://github.com/moby/moby/issues/12997.

We maybe need to look docker config or docker secrets longer term to get
around this.

Hattip to @kevinmcconnell - this was all his idea.

lib/kamal/configuration.rb

@@ -7,7 +7,7 @@ require "net/ssh/proxy/jump"
 
 class Kamal::Configuration
   delegate :service, :image, :servers, :env, :labels, :registry, :stop_wait_time, :hooks_path, to: :raw_config, allow_nil: true
-  delegate :argumentize, :argumentize_env_with_secrets, :optionize, to: Kamal::Utils
+  delegate :argumentize, :optionize, to: Kamal::Utils
 
   attr_accessor :destination
   attr_accessor :raw_config
@@ -113,14 +113,6 @@ class Kamal::Configuration
   end
 
 
-  def env_args
-    if raw_config.env.present?
-      argumentize_env_with_secrets(raw_config.env)
-    else
-      []
-    end
-  end
-
   def volume_args
     if raw_config.volumes.present?
       argumentize "--volume", raw_config.volumes
@@ -174,7 +166,6 @@ class Kamal::Configuration
       repository: repository,
       absolute_image: absolute_image,
       service_with_version: service_with_version,
-      env_args: env_args,
       volume_args: volume_args,
       ssh_options: ssh.to_h,
       sshkit: sshkit.to_h,
@@ -199,12 +190,15 @@ class Kamal::Configuration
 
   # Will raise KeyError if any secret ENVs are missing
   def ensure_env_available
-    env_args
-    roles.each(&:env_args)
+    roles.each(&:env_file)
 
     true
   end
 
+  def host_env_directory
+    "#{run_directory}/env"
+  end
+
   private
     # Will raise ArgumentError if any required config keys are missing
     def ensure_required_keys_present