docs: add Bazel build guide and bzlmod example

[zchuango]

What problem does this PR solve?

Issue Number: resolve #2991

Problem Summary:

The build documentation currently focuses on config_brpc.sh and CMake. It does not provide a clear Bazel/bzlmod build path for users who want to build bRPC or use bRPC as a Bazel dependency.

What is changed and the side effects?

Changed:

• Add Bazel/bzlmod build instructions to the English and Chinese getting started docs.
• Rewrite the English and Chinese Bazel support docs with bzlmod-first dependency guidance.
• Document the required registries and root MODULE.bazel setup for using bRPC as a Bazel dependency.
• Add an echo client target to example/build_with_bazel_module so the bzlmod example has both server and client targets.
• Add required leveldb and openssl single_version_override entries for aarch64 bzlmod builds, and document that users must repeat these overrides in their own root MODULE.bazel.

Side effects:

• Performance effects: None. This PR only changes documentation and the Bazel example.

• Breaking backward compatibility: None.

Validation:

• GitHub Actions passed on PR Brpc cannot link on Ubuntu LTS 16.04 #13.
• Linux x64: Bazel all-options jobs passed with both gcc and clang, including the external bzlmod example under example/build_with_bazel_module.
• macOS ARM64: Bazel build passed.
• Linux aarch64: manually verified with cd example/build_with_bazel_module && bazel-7.2.1 $JVMARG build //:echo_c++_server //:echo_c++_client.

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

Pull request overview

This PR expands bRPC’s Bazel documentation with bzlmod-first guidance and updates the example/build_with_bazel_module example so it builds both an echo server and a new echo client target against a local bRPC checkout.

Changes:

• Add Bazel build instructions to English/Chinese getting started docs and rewrite Bazel support docs with bzlmod-first setup and required registry guidance.
• Extend example/build_with_bazel_module to include an echo_c++_client cc_binary and supporting client.cpp.
• Add bzlmod single_version_override entries (leveldb/openssl) to support aarch64 builds in the bzlmod example.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
example/build_with_bazel_module/MODULE.bazel	Adds bzlmod overrides for leveldb/openssl alongside local brpc checkout usage.
example/build_with_bazel_module/client.cpp	Introduces a Bazel/bzlmod-built echo client example.
example/build_with_bazel_module/BUILD.bazel	Adds a new echo_c++_client cc_binary target.
docs/en/getting_started.md	Adds a “Compile brpc with Bazel” section pointing to the bzlmod example and Bazel docs.
docs/en/bazel_support.md	Rewrites Bazel support docs to emphasize bzlmod usage and provides example MODULE.bazel snippets.
docs/cn/getting_started.md	Adds a Bazel build section mirroring the English getting started guide.
docs/cn/bazel_support.md	Rewrites Chinese Bazel support docs with bzlmod-first guidance and example snippets.

Suppressed comments (3)

docs/en/bazel_support.md:11

• These bazel run commands imply the example is runnable out-of-the-box, but the server requires TLS cert/key files (cert.pem/key.pem). Consider limiting this snippet to build instructions (or add explicit steps to provide/generate the certs).

$ cd example/build_with_bazel_module
$ bazel build //:echo_c++_server //:echo_c++_client
$ bazel run //:echo_c++_server &
$ bazel run //:echo_c++_client

docs/cn/bazel_support.md:10

• 这里的 bazel run 会让读者以为示例可以直接运行，但 server 需要 cert.pem/key.pem。建议这段只保留 build 命令，或补充如何准备证书文件。

$ cd example/build_with_bazel_module
$ bazel build //:echo_c++_server //:echo_c++_client
$ bazel run //:echo_c++_server &
$ bazel run //:echo_c++_client

example/build_with_bazel_module/client.cpp:74

• Use nullptr (C++11+) instead of NULL for the done callback argument, matching other examples (e.g. example/echo_c++/client.cpp) and avoiding the macro’s ambiguous type.

        // Because `done'(last parameter) is NULL, this function waits until
        // the response comes back or error occurs(including timedout).
        stub.Echo(&cntl, &request, &response, NULL);

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