Fixes #37058 - Optimize query to identify orphaned content units

[jpasqualetto]

What are the changes introduced in this pull request?

Optimizes query used to identify orphaned content units

Considerations taken when implementing this change?

Query generated by the method was slow and inefficient. This attempts to offer an alternative with better performance.

What are the testing steps for this pull request?

Execution time of Remove Orphans task should improve drastically.

[chris1984]

ACK, looks fine to me but would prefer someone from team content to look. @ianballou can you take a look or Samir?

[parthaa]

Copy pasting testing steps from
#10638 (comment)

0. Check Katello::Rpm.count in foreman-rake console.
1. Create a lot of orphaned content. You can create these by running below in foreman-rake console:

i = 1
while(i<50000)
f = Katello::Rpm.new(name: i, pulp_id: i)
f.save!
i +=1
end

2. Check Katello::Rpm.count in console.
3. Run bundle exec rails katello:delete_orphaned_content . Go to foreman task in UI and wait for it to complete.
4. Check Katello::Rpm.count again. The orphaned dummy rpm records should get cleaned up..

[chris1984]

Runs much faster, thanks @jpasqualetto