services: set systemd list options as list values

This makes our list definitions mergeable with custom list values
set by users.
Previously, a module error ("value is a string while a list
was expected") was thrown instead.

This commit was partly auto-generated with this script:

#!/usr/bin/env ruby
Dir["**/*.nix"].each do |file|
  src = File.read(file)
  fixed = src.gsub(/ReadWritePaths *= *(.*?);/) do
    "ReadWritePaths = [ #{$1} ];"
  end
  File.write(file, fixed) if fixed != src
end

modules/joinmarket.nix

@@ -328,7 +328,7 @@ in {
         User = cfg.user;
         Restart = "on-failure";
         RestartSec = "10s";
-        ReadWritePaths = cfg.dataDir;
+        ReadWritePaths = [ cfg.dataDir ];
       } // nbLib.allowedIPAddresses cfg.tor.enforce;
     };
 
@@ -368,7 +368,7 @@ in {
         # because it provides the wallet password via stdin to the main process
         SyslogIdentifier = "joinmarket-yieldgenerator";
         User = cfg.user;
-        ReadWritePaths = cfg.dataDir;
+        ReadWritePaths = [ cfg.dataDir ];
       } // nbLib.allowTor;
     };
   })