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/runner_test.go

@@ -121,6 +121,8 @@ func TestRunEvent(t *testing.T) {
 		{"testdata", "issue-598", "push", "", platforms, ""},
 		{"testdata", "env-and-path", "push", "", platforms, ""},
 		{"testdata", "outputs", "push", "", platforms, ""},
+		{"testdata", "steps-context/conclusion", "push", "", platforms, ""},
+		{"testdata", "steps-context/outcome", "push", "", platforms, ""},
 		{"../model/testdata", "strategy", "push", "", platforms, ""}, // TODO: move all testdata into pkg so we can validate it with planner and runner
 		// {"testdata", "issue-228", "push", "", platforms, ""}, // TODO [igni]: Remove this once everything passes