Add --orphan option to fisher or fisher search to list packages installed with a custom url

[ghost]

ls $fisher_cache

The above is not terribly bad as a simple way to query the cache, but it would be nice if we could get a list of those packages that were installed using a custom URL. I think a memorable name could be --orphan.

➡️ This option would be essentially used to add completion to fisher update/uninstall.

Explanation: The current fisher search --select=cache displays all the packages that exist in the cache that Fisherman recognizes and skips those that were installed with a custom URL. The --orphan would show those packages too.