Create Orbit variant of developer_unstable flow
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## Problem to solve
We want to be able to test how the duo developer benefits from our knowledge graph (Orbit). We don't yet know how to best instruct the developer or how to integrate orbit fully but we want to make first steps to allow us testing things.
With this issue, we want to introduces a specialized developer flow on the AI Gateway that knows how to interact with Orbit (the knowledge graph).
In a follow-up https://gitlab.com/gitlab-org/gitlab/-/work_items/599229 we will create a feature flag that would point the developer flow to the flow created with this issue.
## Proposal
Create a new flow version `2.0.0-orbit.yml` (we should double-check that the semantic versions support the suffix) under `duo_workflow_service/agent_platform/experimental/flows/configs/developer/` which is a copy of `duo_workflow_service/agent_platform/experimental/flows/configs/developer/2.0.0.yml` for now but enriched with some orbit instructions as done here https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist/-/merge_requests/5395
NOTE: `duo_workflow_service/agent_platform/experimental/flows/configs/developer/2.0.0.yml` currently also symlinks to `duo_workflow_service/agent_platform/experimental/flows/configs/developer_unstable/1.0.0.yml` since GitLab rails does not yet support the new flow versioning. We should probably do something similar so that the planned feature flag can point to `developer_orbit/experimental` (which maps to `.../experimental/flows/configs/developer_orbit/1.0.0.yml` as a starting point where `developer_orbit/1.0.0.yml` is just a symlink to the `2.0.0-orbit.yml` so that we don't need to maintain things in 2 places and can delete the symlink as soon as flow versioning is supported and the feature flag is adjusted.
## Checklist
* `2.0.0-orbit.yml` exists (as source of truth + symlinked `developer_orbit/1.0.0.yml`)
* A `ai_gateway/prompts/definitions/common/orbit_skill/1.0.0.jinja` exists as proposed in https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist/-/merge_requests/5395/diffs?file_path=ai_gateway%2Fprompts%2Fdefinitions%2Fcommon%2Forbit_skill%2F1.0.0.jinja#2e1c55e8bbe8125c9a085201a5a7538fc31a6012
* `2.0.0-orbit.yml` integrates a orbit skill section in its system prompt (`{% include 'common/orbit_skill/1.0.0.jinja' %}` )
## Links / references
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