Dependency Proxy workhorse migration for image manifests

Context

You can use the dependency proxy to proxy and cache container images from docker hub. When you cache an image/tag, it includes a blob(s) and manifest. In #335563 (closed) we updated the dependency proxy to use workhorse and we focused on blobs since the blobs are much larger than manifests which are typically small.

Problem to solve

Following #335563 (closed) update the dependency proxy to use workhorse for image manifests.

Relevant links

• Parent Issue
• Workhorse counterpart issue
• Sequence diagram

Implementation plan

• Update the DependencyProxyForContainersController to use send_dependency for manifests to be pulled via workhorse.
• This change should be behind a feature flag

Testing and Availability

We have end-to-end tests for dependency proxy features. These tests should be passing after this implementation. To verify that we run package-and-qa on the MRs. No end-to-end test refactoring is needed.