Object store AWS/S3 client and gRPC misconfiguration

**Describe the bug**
:warning: I understand that this is a very niche issue, but I thought I share this trap with others.

If you accidentally point an S3 `object_store` client to an gRPC endpoint, it will happily read empty objects for most paths (i.e. all paths that are not covered by the gRPC endpoint). This can become quite a debug nightmare.

**To Reproduce**
Set up a gRPC server, e.g. w/ `tonic`. The code example for the client sets this up to port `1234`.

Then configure an S3 Client to point at it. It's important that you
- [force the client to use HTTP/2](https://docs.rs/object_store/latest/object_store/struct.ClientOptions.html#method.with_http2_only), otherwise it cannot connect to gRPC over HTTP/2 in the first place
- if your server doesn't run over TLS, you need to [allow HTTP](https://docs.rs/object_store/latest/object_store/struct.ClientOptions.html#method.with_allow_http).
- you may also want to [skip signature checks](https://docs.rs/object_store/latest/object_store/aws/struct.AmazonS3Builder.html#method.with_skip_signature)

```rust
let store = object_store::aws::AmazonS3Builder::new()
.with_bucket_name("dummy")
.with_client_options(
object_store::ClientOptions::new()
.with_allow_http(true)
.with_http2_only(),
)
.with_endpoint("http://localhost:1234")
.with_skip_signature(true)
.build()
.unwrap();
```

**Expected behavior**
I was naively expecting the client to error.

**Additional context**
gRPC for some bizarre reasons decides to not use the HTTP status code at all but instead a custom response header `grpc-status`. In our case, this is set to `12` for `UNIMPLEMENTED`, see
https://grpc.github.io/grpc/core/md_doc_statuscodes.html .

The response body for `UNIMPLEMENTED` is empty. The `content-length` response header is set to `0` (that's required by the `object_store` client).

:arrow_right: So I think what we could do as some kind of safeguard would be to check the `grpc-status` response header and bail out if it is set.

The issue names no source file or test. Start by reproducing the S3 client configuration against a tonic gRPC endpoint, then trace how object_store handles the HTTP response and the grpc-status header. Done means an UNIMPLEMENTED gRPC response is reported as an error instead of being treated as an empty object.

Written by the indexing model from the issue text.