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/accessory.rb

@@ -1,5 +1,5 @@
 class Kamal::Configuration::Accessory
-  delegate :argumentize, :argumentize_env_with_secrets, :optionize, to: Kamal::Utils
+  delegate :argumentize, :env_file_with_secrets, :optionize, to: Kamal::Utils
 
   attr_accessor :name, :specifics
 
@@ -45,8 +45,20 @@ class Kamal::Configuration::Accessory
     specifics["env"] || {}
   end
 
+  def env_file
+    env_file_with_secrets env
+  end
+
+  def host_env_directory
+    File.join config.host_env_directory, "accessories"
+  end
+
+  def host_env_file_path
+    File.join host_env_directory, "#{service_name}.env"
+  end
+
   def env_args
-    argumentize_env_with_secrets env
+    argumentize "--env-file", host_env_file_path
   end
 
   def files

lib/kamal/configuration/role.rb

@@ -1,5 +1,5 @@
 class Kamal::Configuration::Role
-  delegate :argumentize, :argumentize_env_with_secrets, :optionize, to: Kamal::Utils
+  delegate :argumentize, :env_file_with_secrets, :optionize, to: Kamal::Utils
 
   attr_accessor :name
 
@@ -31,8 +31,20 @@ class Kamal::Configuration::Role
     end
   end
 
+  def env_file
+    env_file_with_secrets env
+  end
+
+  def host_env_directory
+    File.join config.host_env_directory, "roles"
+  end
+
+  def host_env_file_path
+    File.join host_env_directory, "#{[config.service, name, config.destination].compact.join("-")}.env"
+  end
+
   def env_args
-    argumentize_env_with_secrets env
+    argumentize "--env-file", host_env_file_path
   end
 
   def health_check_args