Use group-level service account to start foundational Duo workflows

What does this MR do and why?

Start foundational flows with the top-level service account attached to the root group instead of instance-wide @duo-developer service account.

References

Resolve Align DAP Duo Code Review with standard DAP ide... (#580315)

How to set up and validate locally

• Seed the database with foundational flows: Ai::Catalog::Flows::SeedFoundationalFlowsService.new(current_user: User.first, organization: Organizations::Organization.first).execute
• Enable Duo Code Review on DAP: Feature.enabled?(:duo_code_review_on_agent_platform)
• Create a new group
• Create a new project under that group
• Enable the Duo Code Review foundational flow under the group settings
  • This will create a service account
• Create a MR under that project
• Request a review from @GitLabDuo
• Check the DAP pipeline created, it should be created by the service account created above, not the instance-wide @duo-developer

MR acceptance checklist

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