Enable gRPC compression for the BES

### Description of the feature request:

BES events can get pretty large (e.g. if a requested target contains many "important artifacts") and may benefit from compression. It does look like the gRPC backend for the BES doesn't enable any kind of transport layer compression - could this be changed? Does Blaze compress the events?

### Which category does this issue belong to?

_No response_

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

Large BES events can consume non-negligible upload bandwidth.

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

_No response_

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

_No response_

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

_No response_

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

```text

```

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

_No response_

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

_No response_

The issue does not name files or tests; locate the BES gRPC backend and its transport configuration, then inspect how compression is currently handled and whether Blaze compresses events. Done means enabling gRPC transport compression for BES uploads and verifying that large BES events use compression without breaking event delivery.

Written by the indexing model from the issue text.