Support EDITOR having arguments in encrypted secrets codebase

The following discussion from !136002 (merged) should be addressed:

• @stanhu started a discussion: (+1 comment)

  I ran this Rake task and got:

  WARNING: Content was not a valid Redis secret yml file. Did not include any key-value pairs
  Contents were unchanged.
  File encrypted and saved.

  It did create shared/encrypted_settings/redis.yaml.enc, but I expected to see an edit prompt. I think it's because my EDITOR prompt is set to emacs -nw, so system didn't run:

  [42, 51] in /Users/stanhu/gdk-ee/gitlab/lib/gitlab/encrypted_command_base.rb
     42:           contents = encrypted_file_template unless File.exist?(encrypted.content_path)
     43:           File.write(temp_file.path, contents)
     44:           system(ENV['EDITOR'], temp_file.path)
     45:           changes = File.read(temp_file.path)
     46:           contents_changed = contents != changes
  => 47:           validate_contents(changes)
     48:           changes
     49:         end
     50:
     51:         puts "Contents were unchanged." unless contents_changed
  (byebug) encrypted_file_template
  "# password: '123'\n"
  (byebug)

  This might be a follow-up issue, but:

  1. Should we check the return value of system?
  2. Should we use ENV['EDITOR']&.split so that multiple arguments are handled?