Support consolidated object storage configuration

This adds support for the gitlab.yml changes in gitlab!34460 (merged). This allows GitLab to use the Workhorse S3 client with a single credential, enabling proper MD5 checksums and multipart uploads, and paves the way for user-specified keys for encrypted buckets.

These changes require gitlab!35480 (merged) to work.

• Closes #5263 (closed)
• Closes #5447 (closed)
• Closes gitlab-workhorse#222 (closed)
• Closes gitlab-workhorse#210 (closed)

Testing Matrix

Object store provider	Pass?
AWS S3	✅
Oracle Cloud S3	✅
Digital Ocean Spaces	✅
OpenStack Swift	✅

Example config

gitlab_rails['object_store']['enabled'] =  true
gitlab_rails['object_store']['connection'] = {
  'provider' => 'AWS',
  'region' => 'ams3',
  'aws_access_key_id' => 'REDACTED',
  'aws_secret_access_key' => 'REDACTED',
  'endpoint' => 'https://ams3.digitaloceanspaces.com',
}

gitlab_rails['object_store']['proxy_download'] = false
gitlab_rails['object_store']['objects']['artifacts']['bucket'] = 'stanhu-artifacts'
gitlab_rails['object_store']['objects']['external_diffs']['bucket'] = 'stanhu-external-diffs'
gitlab_rails['object_store']['objects']['lfs']['bucket'] = 'stanhu-lfs'
gitlab_rails['object_store']['objects']['uploads']['bucket'] = 'stanhu-uploads'
gitlab_rails['object_store']['objects']['packages']['bucket'] = 'stanhu-packages'
gitlab_rails['object_store']['objects']['dependency_proxy']['bucket'] = 'stanhu-dependency-proxy'
gitlab_rails['object_store']['objects']['terraform_state']['bucket'] = 'stanhu-terraform-state'