Create migration for onboarding dot com instance to Duo Workflow settings

Description

As discussed in !183510 (comment 2437245192) we should be onboarding Duo Workflow for GitLab.com instance via a migration instead of the standard UI proposed in #514388 (closed)

Implementation Plan

• Create a one time migration to create service account user and composite identity oauth application. Similar to

# select organization or default
organization_id = Organizations::Organization::DEFAULT_ORGANIZATION_ID
organization = Organizations::Organization.find_by_id(organization_id)
service = Ai::DuoWorkflows::OnboardingService.new(current_user: admin_user, organization: organization)
service.execute