nixos/lib/make-options-doc: generate asciidoc/md in derivations

use the json file derivation we already have to also generate the asciidoc and
md options docs instead of formatting the options in nix. docbook docs are
already produced in derivations.

the new script produce the exact same output as the old in-nix generation.

nixos/lib/make-options-doc/generateCommonMark.py

@@ -0,0 +1,27 @@
+import json
+import sys
+
+options = json.load(sys.stdin)
+for (name, value) in options.items():
+    print('##', name.replace('<', '\\<').replace('>', '\\>'))
+    print(value['description'])
+    print()
+    if 'type' in value:
+        print('*_Type_*:')
+        print(value['type'])
+        print()
+    print()
+    if 'default' in value:
+        print('*_Default_*')
+        print('```')
+        print(json.dumps(value['default'], ensure_ascii=False, separators=(',', ':')))
+        print('```')
+    print()
+    print()
+    if 'example' in value:
+        print('*_Example_*')
+        print('```')
+        print(json.dumps(value['example'], ensure_ascii=False, separators=(',', ':')))
+        print('```')
+    print()
+    print()