[FeatureRequest] Support ZSTD encoding for HTTP remote cache server

### Description of the feature request:

The common remote-cache server software `bazel-remote` supports ZSTD encoding on both HTTP and GRPC protocols, and it can even store ZSTD-compressed casblobs and then serve them directly to HTTP clients.

So `bazel` may also support the `Accept-Encoding: zstd` HTTP requests (besides `gzip`), just like what https://github.com/bazelbuild/bazel/pull/14041 has added into GPRC requests.

### Which category does this issue belong to?

Remote Execution

### What underlying problem are you trying to solve with this feature?

To make HTTP traffic much smaller and also faster.
If a remote-cache server is `bazel-remote`, `Accept-Encoding: zstd` will also save the server's CPU and power.

### Which operating system are you running Bazel on?

Ubuntu 20.04 LTS (in docker)

### What is the output of `bazel info release`?

release 6.5.0; while `master` on 2024-08-29 still lacks such feature

### If `bazel info release` returns `development version` or `(@non-git)`, tell us how you built Bazel.

N/A

### What's the output of `git remote get-url origin; git rev-parse HEAD` ?

```text
Private repos of my work office
```

### Have you found anything relevant by searching the web?

https://github.com/bazelbuild/bazel/issues/13344
https://github.com/bazelbuild/bazel/pull/14041

### Any other information, logs, or outputs that you want to share?

`src/main/java/com/google/devtools/build/lib/remote/GrpcCacheClient.java` has ZSTD-decompression support;
while `src/main/java/com/google/devtools/build/lib/remote/http/HttpCacheClient.java` uses `io.netty.handler.codec.http.HttpContentDecompressor`, which only recognizes `gzip` and `deflate` as said in https://netty.io/4.0/api/io/netty/handler/codec/http/HttpContentDecompressor.html.

Start with src/main/java/com/google/devtools/build/lib/remote/http/HttpCacheClient.java and compare its HTTP decompression path with src/main/java/com/google/devtools/build/lib/remote/GrpcCacheClient.java and PR 14041. Check how Netty's HttpContentDecompressor handles encodings, then identify the relevant remote-cache tests. Done means HTTP cache requests can negotiate zstd and correctly consume zstd responses alongside existing encodings.

Written by the indexing model from the issue text.