Mapping workflow_dispatch inputs into the Expression inputs context (#1363)

* test: check workflow_dispatch inputs

This implements a test to check for `workflow_dispatch` inputs.
This will be a prerequisite for implementing the inputs.

* feat: map workflow_dispatch input to expression evaluator

This changes adds the workflow_dispatch event inputs
to the `inputs` context and maintaining the boolean type

* fix: coerce boolean input types

* fix: use step env if available, rc env otherwise

pkg/runner/testdata/workflow_dispatch/event.json

@@ -0,0 +1,6 @@
+{
+  "inputs": {
+    "required": "required input",
+    "boolean": "true"
+  }
+}