Investigate how to create a Duo Agent Platform flow for code review

What is the goal of this spike?

Investigate how to create a Duo Agent Platform flow that has all capabilities of existing Duo Code Review feature. This flow will eventually replace the Duo Code Review functionality in the near future.

Scope/MVC

• Have a bare minimum flow that can be used to triggered via command line (https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist/-/tree/main/docs/flow_registry#debugging-flows) when Duo Code Review bot is assigned to a MR
• The flow should gather the same context currently supported by Duo Code Review:
  • git diff of all modifications
  • modified files content before modications
  • MR title
  • MR description
  • eventual custom instructions included in the project (out of the scope of the spike)

Acceptance criteria

At the end of the spike, we should have a base flow that calls the LLM to perform the code review. No need to actually add comments to the MR.