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

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[verbanicm]

@hawkeye-sama Thanks for fixing!