GraphQL API for listing all workflows for a user

What does this MR do and why?

The MR adds a new GraphQL endpoint to return all workflows belonging to the current user.

This MR adds a new scope Ai::DuoWorkflows::Workflow.for_user. A sample query of this scope is as follows:

SELECT "duo_workflows_workflows".* FROM "duo_workflows_workflows" WHERE "duo_workflows_workflows"."user_id" = 1

Query plan from postgres.ai.

Note that there are no workflows in the production thus this query returns 0 rows.

 Seq Scan on public.duo_workflows_workflows  (cost=0.00..0.00 rows=1 width=42) (actual time=0.027..0.027 rows=0 loops=1)
   Filter: (duo_workflows_workflows.user_id = 1614863)
   Rows Removed by Filter: 0
   I/O Timings: read=0.000 write=0.000

Recommendations: ✅ Looks good

Summary

Time: 0.796 ms  
  - planning: 0.722 ms  
  - execution: 0.074 ms  
    - I/O read: 0.000 ms  
    - I/O write: 0.000 ms  
  
Shared buffers:  
  - hits: 0 from the buffer pool  
  - reads: 0 from the OS file cache, including disk I/O  
  - dirtied: 0  
  - writes: 0  

Explain in rails console from local environment

I'm also adding this as there are no workflow records in postgres.ai

Ai::DuoWorkflows::Workflow.for_user(1).explain
  Ai::DuoWorkflows::Workflow Load (1.0ms)  SELECT "duo_workflows_workflows".* FROM "duo_workflows_workflows" WHERE "duo_workflows_workflows"."user_id" = 1 
=> EXPLAIN for: SELECT "duo_workflows_workflows".* FROM "duo_workflows_workflows" WHERE "duo_workflows_workflows"."user_id" = 1 
                                                       QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------
 Index Scan using index_duo_workflows_workflows_on_user_id on duo_workflows_workflows  (cost=0.15..6.26 rows=6 width=42)
   Index Cond: (user_id = 1)
(2 rows)

MR acceptance checklist

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Screenshots or screen recordings

How to set up and validate locally

1. Enable FF start_duo_workflows
2. Create a duo workflow for a project you have developer access

curl -XPOST -i http://gdk.test:3000/api/v4/ai/duo_workflows/workflows\?private_token\=[YOUR_TOKEN]\&project_id\=[PROJECT_ID]

1. Visit http://gdk.test:3000/-/graphql-explorer
2. Run the following query.

query getDuoWorkflowWorkflows {
  duoWorkflowWorkflows {
    edges {
      node {
        id,
        projectId,
        userId,
        humanStatus,
        createdAt,
        updatedAt
      }
    }
  }
}

Related to #469451 (closed)