git-cat-file: Support for reading object type and content from a remote without downloading them

Once we are in a world where we have blobs offloaded to promisor remotes, it would be nice to enable Git to access objects directly through git-cat-file(1) without having to download the entire object to do so.

https://lore.kernel.org/git/20220728230210.2952731-7-calvinwan@google.com/ was a patch series that attempted to enable a new option remote-object-info is based on the same basic idea. (this topic got dropped at some point though from lack of activity).

What if we had a mode --allow-promisor=missing or something like that such that when git-cat-file(1) cannot find an object in the database, it will try looking on promisor remotes.

git-cat-file(1) is the underlying Git call for a lot of repository access from the Rails application. If we could allow git-cat-file(1) to access objects from promisor remotes and stream them to the client, it would be more efficient for repositories where the bulk of objects live on object storage.