Update angular-devkit to v13

[christian-bromann]

The upgrade from Angular DevKit from v12 to v13 included some breaking changes particular around the JSON parser. They have removed the public API that we use in json.ts:

import {
  JsonAstArray,
  JsonAstKeyValue,
  JsonAstNode,
  JsonAstObject,
  JsonValue,
  JsonParseMode,
  parseJsonAst
} from '@angular-devkit/core';

They recommend to use a separate JSON parser. Any contributions that resolves the bug are highly appreciated. Please take a look into our contribution guidelines and let us know if you have any questions. Cheers!