Feature: Add `in-toto` support to `complyctl`

[trevor-vaughan]

Is your feature request related to a problem? Please describe.

As part of preparing the acceptance tests for #678, I discovered that we didn't have any in-toto attestation support in the tooling.

This isn't a huge gap since users can wrap and validate the material independently if they like but it would be nice to have as a native capability for a seamless UX.

Describe the solution you'd like

Leaving this open to the implementer. All that I would ask is that full acceptance tests be added to validate the workflow.

Describe alternatives you've considered

None

Additional context

None

[marcusburghardt]

@trevor-vaughan could you elaborate more details on the desired feature and the problem it would solve so we can better assess the priority and effort of this issue, please?