Remove fog-aws and fog-core, complete fog removal

[kathap]

Remove the last remaining fog gems (fog-aws, fog-core) and all fog blobstore code. All other fog gems (fog-azure-rm, fog-google, fog-aliyun) were previously removed. storage-cli is the default blobstore backend and has fully replaced fog. Removing fog-aws and fog-core also drops their transitive deps (fog-json, fog-xml), completing the fog removal and reducing Dependabot maintenance burden.

A short explanation of the proposed change

This change removes the last two fog gems (fog-aws, fog-core) and deletes all remaining fog-based blobstore code from the Cloud Controller. The fog client, blob, CDN, and provider classes under lib/cloud_controller/blobstore/fog/ are deleted, and the fog branch is removed from the blobstore ClientProvider so storage-cli is now the sole blobstore backend. All fog_connection / fog_aws_storage_options config keys are dropped from the config schemas and YAML fixtures, and the legacy fog-provider translation (AWS→s3, webdav→dav) is removed from StorageCliClient.

The test suite is migrated off fog accordingly: Fog.mock! and AWS credential fixtures are replaced with a real local blobstore, blob test-doubles that pointed at the deleted FogBlob now use LocalBlob, and two shared contexts ('a remote blobstore', 'a seeded empty-file resource') centralize the setup that fog's global mock used to provide implicitly. A few local-blobstore correctness fixes surfaced during the migration are included (LocalBlob#content_length returns an Integer, LocalClient#delete_all respects root_dir).

An explanation of the use cases your change solves

• Completes the fog removal effort. fog-azure-rm, fog-google, and fog-aliyun were already removed; this drops the final fog-aws/fog-core dependencies (and their transitive fog-json/fog-xml), so the codebase no longer ships or loads any fog code.
• Reduces maintenance and security burden. Eliminating the fog gems removes a recurring source of Dependabot/CVE churn from unmaintained transitive dependencies.
• Single, consistent blobstore backend. With storage-cli as the only backend, operators no longer configure fog_connection; blobstore behavior is uniform across AWS/GCS/Azure/WebDAV via storage-cli, simplifying configuration and the code paths that had to branch on fog vs. storage-cli.
• Keeps the test suite honest. Tests now exercise the real local blobstore instead of fog's in-memory mock, so blobstore behavior under test matches what actually ships.

Changes:

• Remove fog-aws and fog-core from Gemfile/Gemfile.lock (drops transitive fog-json, fog-xml)
• Delete lib/cloud_controller/blobstore/fog/ entirely (FogClient, FogBlob, Cdn, providers)
• Remove the fog branch and require from blobstore ClientProvider
• Remove fog_connection / fog_aws_storage_options config keys from all schemas (api, worker, clock, deployment_updater, blobstore_benchmarks) and YAML
  fixtures (cloud_controller.yml, bosh-lite.yml, port_8181_config.yml)
• Remove legacy fog provider translation from StorageCliClient (AWS→s3, webdav→dav)
• Fix LocalBlob#content_length to return Integer instead of String
• Fix LocalClient#delete_all to respect root_dir
• Add require 'null_blob' to null_client.rb (fog specs previously loaded it transitively)
• Update README and ADR-0014; drop deleted fog paths from .rubocop_todo.yml

Test infrastructure (fog → local blobstore):

• Replace Fog.mock! and AWS fog_connection credentials with local blobstore config in spec_helper_helper.rb and test_config.rb
• Add spec/support/blobstore/shared_contexts.rb — 'a remote blobstore' (non-local blobstore stub for redirect tests) and 'a seeded empty-file resource'
  (resource-pool SHA seed)
• Update blob doubles from the deleted FogBlob to LocalBlob across affected specs
• Delete all fog specs under spec/unit/lib/cloud_controller/blobstore/fog/

• Links to any other associated PRs
  Remove fog provider support  capi-release#671
  Remove fog google blobstore support #5261
  Remove fog aliyun blobstore support #5154
  Remove fog-local and fog-openstack blobstore support #5197
  Remove fog azure support from ccng coding and Gemfile #5118

• I have reviewed the contributing guide

• I have viewed, signed, and submitted the Contributor License Agreement

• I have made this pull request to the main branch

• I have run all the unit tests using bundle exec rake

• I have run CF Acceptance Tests

[johha]

LGTM 🚀