* add support for action queries
* a new parameter `type` is added in the ArgumentDefinition, its value
can be either `query` or `mutation` and it defaults to the latter
* throw 400 when a query action is tried to explain
* update the actions docs to include query actions
* refactor the ToJSON and ToOrdJSON of ActionDefinition
Co-authored-by: Rishichandra Wawhal <rishi@hasura.io>
Co-authored-by: Tirumarai Selvan <tiru@hasura.io>
