Return $metadata resource as odata + openapi spec

Returning odata and openapi specs in json format.
Specs are scoped to the request permissions.
Different users (roles) will receive different metadata endpoints
and resources.

Change-type: minor
Signed-off-by: Harald Fischer <harald@balena.io>

Author: fisehara

package.json

@@ -61,6 +61,7 @@
     "express-session": "^1.17.3",
     "lodash": "^4.17.21",
     "memoizee": "^0.4.15",
+    "odata-openapi": "^0.18.1",
     "pinejs-client-core": "^6.10.2",
     "randomstring": "^1.2.2",
     "typed-error": "^3.2.1"