Add needs job output (#629)

* Add outputs field to job model

* Add output interpolation for jobs

* Add otto config reference for interpolated job output values into 'needs' context

* Add output interpolation call after job has completed.

* gofmt

* Remove whitespace

* goimports

Co-authored-by: Casey Lee <cplee@nektos.com>

pkg/model/workflow.go

@@ -66,6 +66,7 @@ type Job struct {
 	Strategy       *Strategy                 `yaml:"strategy"`
 	RawContainer   yaml.Node                 `yaml:"container"`
 	Defaults       Defaults                  `yaml:"defaults"`
+	Outputs        map[string]string         `yaml:"outputs"`
 }
 
 // Strategy for the job