feat: add interactive task inputs

[roele]

Rough draft to add support for interactive task inputs.

Open topics up for discussion are:

• TOML schema
  • do we need specific schema types for each input?
• parallel tasks
  • only support linear tasks or job=1?
• handling for non-interactive usage
  • skip inputs if -y is passed?
  • scripts could fallback to default values if environment variable is not set