Add open api spec to documentation
NB: For the schema name with generated id at the end, there is currently an issue on github to solve this : https://github.com/ePages-de/restdocs-api-spec/issues/78
NB: For the schema name with generated id at the end, there is currently an issue on github to solve this : https://github.com/ePages-de/restdocs-api-spec/issues/78