treewide: automatically md-convert option descriptions

the conversion procedure is simple:

 - find all things that look like options, ie calls to either `mkOption`
   or `lib.mkOption` that take an attrset. remember the attrset as the
   option
 - for all options, find a `description` attribute who's value is not a
   call to `mdDoc` or `lib.mdDoc`
 - textually convert the entire value of the attribute to MD with a few
   simple regexes (the set from mdize-module.sh)
 - if the change produced a change in the manual output, discard
 - if the change kept the manual unchanged, add some text to the
   description to make sure we've actually found an option. if the
   manual changes this time, keep the converted description

this procedure converts 80% of nixos options to markdown. around 2000
options remain to be inspected, but most of those fail the "does not
change the manual output check": currently the MD conversion process
does not faithfully convert docbook tags like <code> and <package>, so
any option using such tags will not be converted at all.

nixos/modules/services/admin/meshcentral.nix

@@ -7,7 +7,7 @@ in with lib; {
   options.services.meshcentral = with types; {
     enable = mkEnableOption "MeshCentral computer management server";
     package = mkOption {
-      description = "MeshCentral package to use. Replacing this may be necessary to add dependencies for extra functionality.";
+      description = lib.mdDoc "MeshCentral package to use. Replacing this may be necessary to add dependencies for extra functionality.";
       type = types.package;
       default = pkgs.meshcentral;
       defaultText = literalExpression "pkgs.meshcentral";

nixos/modules/services/admin/oxidized.nix

@@ -12,7 +12,7 @@ in
     user = mkOption {
       type = types.str;
       default = "oxidized";
-      description = ''
+      description = lib.mdDoc ''
         User under which the oxidized service runs.
       '';
     };
@@ -20,7 +20,7 @@ in
     group = mkOption {
       type = types.str;
       default = "oxidized";
-      description = ''
+      description = lib.mdDoc ''
         Group under which the oxidized service runs.
       '';
     };
@@ -28,7 +28,7 @@ in
     dataDir = mkOption {
       type = types.path;
       default = "/var/lib/oxidized";
-      description = "State directory for the oxidized service.";
+      description = lib.mdDoc "State directory for the oxidized service.";
     };
 
     configFile = mkOption {
@@ -62,7 +62,7 @@ in
           # ... additional config
         ''';
       '';
-      description = ''
+      description = lib.mdDoc ''
         Path to the oxidized configuration file.
       '';
     };
@@ -76,7 +76,7 @@ in
           # ... additional hosts
         '''
       '';
-      description = ''
+      description = lib.mdDoc ''
         Path to the file/database which contains the targets for oxidized.
       '';
     };

nixos/modules/services/admin/pgadmin.nix

@@ -31,18 +31,18 @@ in
     enable = mkEnableOption "PostgreSQL Admin 4";
 
     port = mkOption {
-      description = "Port for pgadmin4 to run on";
+      description = lib.mdDoc "Port for pgadmin4 to run on";
       type = types.port;
       default = 5050;
     };
 
     initialEmail = mkOption {
-      description = "Initial email for the pgAdmin account.";
+      description = lib.mdDoc "Initial email for the pgAdmin account.";
       type = types.str;
     };
 
     initialPasswordFile = mkOption {
-      description = ''
+      description = lib.mdDoc ''
         Initial password file for the pgAdmin account.
         NOTE: Should be string not a store path, to prevent the password from being world readable.
       '';
@@ -52,9 +52,9 @@ in
     openFirewall = mkEnableOption "firewall passthrough for pgadmin4";
 
     settings = mkOption {
-      description = ''
+      description = lib.mdDoc ''
         Settings for pgadmin4.
-        <link xlink:href="https://www.pgadmin.org/docs/pgadmin4/development/config_py.html">Documentation</link>.
+        [Documentation](https://www.pgadmin.org/docs/pgadmin4/development/config_py.html).
       '';
       type = pyType;
       default= {};

nixos/modules/services/admin/salt/master.nix

@@ -24,7 +24,7 @@ in
       configuration = mkOption {
         type = types.attrs;
         default = {};
-        description = "Salt master configuration as Nix attribute set.";
+        description = lib.mdDoc "Salt master configuration as Nix attribute set.";
       };
     };
   };

nixos/modules/services/admin/salt/minion.nix

@@ -25,9 +25,9 @@ in
       configuration = mkOption {
         type = types.attrs;
         default = {};
-        description = ''
+        description = lib.mdDoc ''
           Salt minion configuration as Nix attribute set.
-          See <link xlink:href="https://docs.saltstack.com/en/latest/ref/configuration/minion.html"/>
+          See <https://docs.saltstack.com/en/latest/ref/configuration/minion.html>
           for details.
         '';
       };