Wrap node commands with Capistrano

This code is based on what the rvm1-capistrano and capistrano-nvm gems
do, but simplified a bit to take advantage of the `fnm exec` command.

Since ExecJS will check for a JavaScript runtime every time the
application is started, we need to include commands like `bundle` (used
when running `bin/delayed_job`), `puma` and `rake`, so Node.js is found
when running these commands. I'm not sure whether `pumactl` is also
necessary, but I've added it for consistency.

We're also including the default commands gems like capistrano-nvm use
because we will add the `npm` command in the near future.

Note that, in order to setup FNM, we need to enter the actual release
folder (using `within release_path` isn't enough). So we have to run
this task after the actual release is created; otherwise many commands
would run in the previous release's folder.

config/deploy.rb

@@ -46,6 +46,7 @@ def main_deploy_server
                             "cd #{release_path} && fnm env > /dev/null && eval \"$(fnm env)\""
                         end
 set :fnm_install_node_command, -> { "#{fetch(:fnm_setup_command)} && fnm use --install-if-missing" }
+set :fnm_map_bins, %w[bundle node npm puma pumactl rake yarn]
 
 set :puma_conf, "#{release_path}/config/puma/#{fetch(:rails_env)}.rb"
 
@@ -59,6 +60,8 @@ def main_deploy_server
   Rake::Task["delayed_job:default"].clear_actions
   Rake::Task["puma:smart_restart"].clear_actions
 
+  after "git:create_release", "map_node_bins"
+
   after :updating, "install_node"
   after :updating, "install_ruby"
 
@@ -120,6 +123,20 @@ def main_deploy_server
   end
 end
 
+task :map_node_bins do
+  on roles(:app) do
+    within release_path do
+      with rails_env: fetch(:rails_env) do
+        prefix = "#{fetch(:fnm_setup_command)} && fnm exec"
+
+        fetch(:fnm_map_bins).each do |command|
+          SSHKit.config.command_map.prefix[command.to_sym].unshift(prefix)
+        end
+      end
+    end
+  end
+end
+
 task :refresh_sitemap do
   on roles(:app) do
     within release_path do