Allow disabling default enum conversions (#3536)

docs/mkdocs/docs/features/enum_conversion.md

@@ -58,3 +58,4 @@ Other Important points:
   default pair carefully.
 - If an enum or JSON value is specified more than once in your map, the first matching occurrence from the top of the
   map will be returned when converting to or from JSON.
+- To disable the default serialization of enumerators as integers and force a compiler error instead, see [`JSON_DISABLE_ENUM_SERIALIZATION`](../api/macros/json_disable_enum_serialization.md).

docs/mkdocs/docs/features/macros.md

@@ -54,6 +54,12 @@ Exceptions can be switched off by defining the symbol `JSON_NOEXCEPTION`.
 
 See [full documentation of `JSON_NOEXCEPTION`](../api/macros/json_noexception.md).
 
+## `JSON_DISABLE_ENUM_SERIALIZATION`
+
+When defined, default parse and serialize functions for enums are excluded and have to be provided by the user, for example, using [`NLOHMANN_JSON_SERIALIZE_ENUM`](../api/macros/nlohmann_json_serialize_enum.md).
+
+See [full documentation of `JSON_DISABLE_ENUM_SERIALIZATION`](../api/macros/json_disable_enum_serialization.md).
+
 ## `JSON_NO_IO`
 
 When defined, headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and `<ostream>` are not included and parse functions