TASK: Review 'placeholder' packages in Content Resolver

[asamalik]

There's a few package placeholders in the ELN Package Set in Content Resolver (search for 'placeholder'). But some of them definitely exist in Fedora ELN. Let's review this and update the workloads.

[yselkowitz]

A few were converted to real packages last year. AFAICS all remaining placeholders are either not in Fedora or are leaves not wanted in ELN (e.g. fence-agents due to its many dependencies, which are bundled in RHEL).