GC prune and git reflog expire scope and related config

We use deferred integration branches which are then preempted and then deleted and recreated. However, the discarded branches leave dangling commits and trees that I can view with this command:git fsck --unreachable --no-reflogs

I could clear them with

git reflog expire --expire-unreachable=now --all
git gc --prune=now

      

        
        
        
      

    

or something similar, but I want to first understand the scope of these commands and the corresponding configuration.

So, specific questions:

• To keep the new clones lean, how can I gc
  
  trim and flush the lists, not just locally, but also in a remote repository hosted on GitHub?
• Can I install the related items git configuration (eg, gc.pruneexpire
  
  , gc.reflogexpire
  
  , gc.reflogexpireunreachable
  
  ) to accommodate the repository GitHub?

PS: See here for useful context: Git listing and deletion ends up with no branch (dangling?)