Add more steps context support (#887)

* feat: add more steps context support

- Add step outcome
- Remove step success in favour of conclusion

* feat: add conclusion and outcome steps context tests

Add corresponding tests and extend pkg/runner/expression.go vmSteps() to
handle steps context conclusion and outcome iota as strings.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

pkg/runner/step_context.go

@@ -640,8 +640,8 @@ func (sc *StepContext) execAsComposite(ctx context.Context, step *model.Step, _
 		// Setup the outputs for the composite steps
 		if _, ok := rcClone.StepResults[stepClone.ID]; !ok {
 			rcClone.StepResults[stepClone.ID] = &stepResult{
-				Success: true,
-				Outputs: make(map[string]string),
+				Conclusion: stepStatusSuccess,
+				Outputs:    make(map[string]string),
 			}
 		}