#6201 docker-base: select orchestrator-client .deb by image architecture (#6200)

Fixes #6200.

test/infra/docker-base/Dockerfile hardcoded orchestrator-client_4.31.1_amd64.deb, so proxysql-ci-base failed to build on arm64 (package architecture (amd64) does not match system (arm64)).

• Package architecture now comes from dpkg --print-architecture; both amd64 and arm64 .debs are published for the pinned version (verified both URLs return 200 for v4.31.1 and v4.32.0).
• Version moved to ARG ORCHESTRATOR_CLIENT_VERSION=4.32.0 (kept pinned for reproducible CI images; switching to "latest" can follow once proxysql/orchestrator#130 provides an installer).
• Unsupported architectures fail with an explicit message.

Verification: built a minimal ubuntu:24.04 image with the same RUN snippet on amd64; orchestrator-client installed at /usr/bin/orchestrator-client. Not built on arm64 hardware here.

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Summary by cubic

Fixes the proxysql-ci-base image build on arm64 hosts by selecting the orchestrator-client package based on the image architecture instead of hardcoding amd64.

• Version is now a build ARG, pinned to 4.32.0 (latest release).
• Unsupported architectures fail with a clear error message.

Summary by CodeRabbit

• Build Improvements
  • Docker image builds now select the appropriate orchestrator client package for supported amd64 and arm64 architectures.
  • Builds on unsupported architectures now fail validation.
  • The orchestrator client version can be configured during the build, with version 4.32.0 used by default.