Docs: Added artifact register reader permission required for ci/cd pipeline

[hawkeye-sama]

Hi maintainers. This PR is based on #354

Found an issue that when deploying to App engine via github actions for standard environment, you get logs with this error reason: generic::permission_denied: failed to fetch manifest: generic::permission_denied which is due to Artifact Registry Reader Permission missing from service account used. I did not encounter this issue for flexible environment. Tested with following configurations deploy.yaml ( github workflow )

name: Deploy to GAE

on:
  # Triggers the workflow on push or pull request events but only for the main branch
  push:
    branches: [ main ]

jobs:
  deploy:
    name: Deploying to Google Cloud
    runs-on: ubuntu-latest

    steps:
    - name: Checkout
      uses: actions/checkout@v4

    - name: 'Auth GCP'
      uses: 'google-github-actions/auth@v2'
      with:
        credentials_json: '${{ secrets.GCP_DEPLOY }}'

    - id: deploy
      name: Deploy to App Engine
      uses: google-github-actions/deploy-appengine@v2
      with:
        deliverables: app.yaml
        project_id: ${{ secrets.GCP_PROJECT }}

    - name: Test output
      run: 'curl "${{ steps.deploy.outputs.version_url }}"'

app.yaml

service: default
runtime: nodejs18
env: standard
instance_class: F1

env_variables:
  NODE_ENV: production
  PORT: 8080

inbound_services:
- warmup

automatic_scaling:
  min_instances: 1
  max_instances: 2
  target_cpu_utilization: 0.75

handlers:
- url: /.*
  script: auto
  secure: always
  redirect_http_response_code: 301

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[verbanicm]

@hawkeye-sama Thanks for fixing!