Make `Expand` to retain type for a simple expansions allowing to deep pass entries

Based on: !3 (merged)

This retains when performing simple expansion in a form of "${{ a.b.c }}" to retain underlying type instead of converting to string always. This allows to support following example, since structure is passed in-depth, and sub-step can deep access the relevant object:

- step: step-name
  inputs:
    features:
      ping:
        color: red
      pong:
        color: blue

...
---
type: steps
steps:
  - step: step-name-2
    inputs:
      config: ${{ inputs.features.ping }}

...
---
type: exec
exec:
  command: [echo, "Passed color: ${{inputs.config.color}}"]