[gitlab-org/gitlab] Consolidate duplicate workflow execution services

### ROOT CAUSE The duplication of workflow execution services (`CreateAndStartWorkflowService` and `ExecuteWorkflowService`) stems from overlapping responsibilities and inconsistent parameter handling. This redundancy leads to confusion, maintenance overhead, and bugs, such as environment settings being overwritten. ### CODE FIX To consolidate the duplicate services, follow these steps: 1. **Create a Consolidated Service** - Merge the functionality of both services into a single `WorkflowExecutionService`. - Include parameters from both services, preserving catalog-specific parameters (`json_config`, `additional_context`) while ensuring environment settings respect workflow definitions. 2. **Update Callers** - Modify `ee/app/services/ai/duo_workflows/create_and_start_workflow_service.rb` and `ee/app/services/ai/catalog/execute_workflow_service.rb` to use the new `WorkflowExecutionService`. - Update all dependent flows (AI Catalog, Code Review, Fix Pipeline) to use the consolidated service. 3. **Remove Duplicate Services** - After updating callers, remove the old services to reduce redundancy.

ruby
# New consolidated service
class WorkflowExecutionService
  def initialize(workflow_id, environment: nil, json_config: nil, additional_context: nil)
    @workflow_id = workflow_id
    @environment = environment
    @json_config = json_config
    @additional_context = additional_context
  end

  def execute
    workflow = Workflow.find(@workflow_id)
    workflow_service = workflow.create_service

    workflow_service.create_workflow(
      environment: @environment || workflow.environment,
      json_config: @json_config,
      additional_context: @additional_context
    )
  end
end

# Example of updating a caller
class CodeReviewService
  def process_workflow(workflow_id)
    WorkflowExecutionService.new(workflow_id).execute
  end
end

# Remove old services
# Remove ee/app/services/ai/duo_workflows/create_and_start_workflow_service.rb
# Remove ee/app/services/ai/catalog/execute_workflow_service.rb