Build a WASM-compatible `object_store` alternative

[johnbchron]

We need to be able to access arbitrary object storage from a Cloudflare worker.

Our access pattern for the crate object_store can be found in the first-party storage crate.

Basically, we use a models::StorageCredentials to create some struct that can access the storage that our StorageCredentials are semantically pointing to. Sometimes that's local storage, in which object_store is not involved, but in the case of R2, we do use object_store. Right now, we use get() with streaming, multipart methods, and head() for testing.

The problem is that object_store use reqwest, which uses sockets for networking, i.e. the normal approach. In WASM, we can't really do that. Usually you use browser APIs, but we don't have those either. We have the Fetch API in the worker crate. This is non-standard partially because they couldn't provide browser APIs, and partially because they have to translate it back to JS and send it back through their proxy network as an outbound request.

I think it would be best if you could fork object_store to allow plugging in a different request backend. If reqwest has native support for this, that's the optimal situation. If not, it may work to make the interface sub out reqwest, though that might breach the complexity barrier. If not that, you could just recreate a minified version of object_store in the Nika repo.

[zmontgo]

A quick look at reqwest seems to show that you can't swap out hyper for something else. surf seems to be what we want... according to its docs, Surf is a Rust HTTP client built for ease-of-use and multi-HTTP-backend flexibility

Rebuilding something like reqwest (even just the API we need) would be doable, but definitely a chore, and if we can avoid it, I think that would be best to get the benefits of delegating maintenance. If this suits our needs, I'll fork object_store to nika-industries and build it to work with surf, accepting a different backend at comptime.

[johnbchron]

Make certain that you can get surf to work with the worker API before you work on migrating object_store.

[zmontgo]

This is effectively solved by the addition of the object_store_s3_wasm crate, but it is missing a couple important parts:

1. This has not passed tests on my machine due to an OOM error
2. I am not certain that this plays nicely with our existing infrastructure
3. Crate-level documentation must be created
4. Integration tests with wrangler need to be built

I think the first three are within scope of this issue, but the last one is not. I'm opening a new issue for that.