Add missing 'type', 'defaultText' and 'literalExample' in module definitions

- add missing types in module definitions
- add missing 'defaultText' in module definitions
- wrap example with 'literalExample' where necessary in module definitions

nixos/modules/services/monitoring/nagios.nix

@@ -94,7 +94,9 @@ in
       };
 
       plugins = mkOption {
+        type = types.listOf types.package;
         default = [pkgs.nagiosPluginsOfficial pkgs.ssmtp];
+        defaultText = "[pkgs.nagiosPluginsOfficial pkgs.ssmtp]";
         description = "
           Packages to be added to the Nagios <envar>PATH</envar>.
           Typically used to add plugins, but can be anything.
@@ -102,14 +104,18 @@ in
       };
 
       mainConfigFile = mkOption {
+        type = types.package;
         default = nagiosCfgFile;
+        defaultText = "nagiosCfgFile";
         description = "
           Derivation for the main configuration file of Nagios.
         ";
       };
 
       cgiConfigFile = mkOption {
+        type = types.package;
         default = nagiosCGICfgFile;
+        defaultText = "nagiosCGICfgFile";
         description = "
           Derivation for the configuration file of Nagios CGI scripts
           that can be used in web servers for running the Nagios web interface.