As a user I want to use the REST API on my Wikibase instance, in order to build/use tools which use the content in a Wikibase Cloud instance.
**Current situation**
Wikibase Cloud is currently running 1.39 which is a long way behind Wikidata and therefore the REST API features are different (routes: [1.39](https://github.com/wikimedia/mediawiki-extensions-Wikibase/blob/REL1_39/repo/rest-api/routes.json) - [master](https://github.com/wikimedia/mediawiki-extensions-Wikibase/blob/master/repo/rest-api/routes.json)). Unless we update, before turning this on, we will need to make it clear to users.
**AC**
* update REST API
* enable swagger for each instance
//Hints for devs//
* https://www.wikidata.org/wiki/Wikidata:REST_API
* https://github.com/wikimedia/mediawiki-extensions-Wikibase/tree/master/repo/rest-api
* https://doc.wikimedia.org/Wikibase/master/php/repo_rest-api_README.html ([1.39 version](https://doc.wikimedia.org/Wikibase/REL1_39/php/md_repo_2rest-api_2README.html))