Support consolidated object store configuration

In gitlab!34460 (merged) we added support to consolidate object storage settings in gitlab.yml. This will make it easier to configure credentials/secrets in one place.

Old format

  artifacts:
    path: tmp/tests/artifacts
    enabled: true
    object_store:
      enabled: false
      remote_directory: artifacts # The bucket name
      background_upload: false
      connection:
        provider: AWS
        aws_access_key_id: AWS_ACCESS_KEY_ID
        aws_secret_access_key: AWS_SECRET_ACCESS_KEY
        region: us-east-1

New consolidated format

  object_store:
    enabled: true
    connection:
      provider: AWS
      aws_access_key_id: AWS_ACCESS_KEY_ID
      aws_secret_access_key: AWS_SECRET_ACCESS_KEY
      region: us-east-1
    proxy_download: true
    objects:
      artifacts:
        bucket: artifacts
        proxy_download: false
      external_diffs:
        bucket: external-diffs
      lfs:
        bucket: lfs-objects
      uploads:
        bucket: uploads
      packages:
        bucket: packages
      dependency_proxy:
        bucket: dependency_proxy