Add hydra OpenAPI description (#750)

* Add swagger config

* Add hydra api info to the README

* hydra.yaml: added some more descriptions

* Add /login

* Add 404/403 responses

* hydra.yaml -> hydra-api.yaml

* Address PR comments

- drop releases/releasename
- document dependency
- document defaultpath

* Fix syntax

* Add project creation

Add `PUT /project/{id}`

* Add /search

* Add "/api/jobsets" endpoint

* Add /api/push endpoint

* Add jobset PUT definition

* Add eval endpoint

* Remove duplicated key

* Fix typo

* Fix structural errors

* fix another error

* Link to hydra-api.yaml from master

* Add openapi yaml validation step to CI

README.md

@@ -84,6 +84,10 @@ $ configurePhase # NOTE: not ./configure
 $ make
 ```
 
+### JSON API
+
+You can also interface with Hydra through a JSON API. The API is defined in [hydra.yaml](./hydra.yaml) and you can test and explore via the [swagger editor](https://editor.swagger.io/?url=https://raw.githubusercontent.com/NixOS/hydra/master/hydra-api.yaml)
+
 ## Additional Resources
 
 - [Hydra User's Guide](https://nixos.org/hydra/manual/)