GH-44982: [C++] Add support for building system OpenTelemetry

[kou]

Rationale for this change

We don't need to disallow -Dopentelemetry-cpp_SOURCE=SYSTEM.

What changes are included in this PR?

Remove forcing opentelemetry-cpp_SOURCE=AUTO.

Are these changes tested?

Yes.

Are there any user-facing changes?

Yes.

• GitHub Issue: [C++] Allow building against system opentelemetry #44982

[kou]

@github-actions crossbow submit -g cpp -g linux -g wheel

[github-actions]

⚠️ GitHub issue #44982 has been automatically assigned in GitHub to PR creator.

[kou]

@github-actions crossbow submit -g cpp -g linux -g wheel -g r

[github-actions]

Revision: af95592

Submitted crossbow builds: ursacomputing/crossbow @ actions-eb8d4f214e

Task	Status
almalinux-8-amd64
almalinux-8-arm64
almalinux-9-amd64
almalinux-9-arm64
amazon-linux-2023-amd64
amazon-linux-2023-arm64
centos-7-amd64
centos-8-stream-amd64
centos-8-stream-arm64
centos-9-stream-amd64
centos-9-stream-arm64
debian-bookworm-amd64
debian-bookworm-arm64
debian-trixie-amd64
debian-trixie-arm64
example-cpp-minimal-build-static
example-cpp-minimal-build-static-system-dependency
example-cpp-tutorial
python-sdist
r-binary-packages
r-recheck-most
test-alpine-linux-cpp
test-build-cpp-fuzz
test-conda-cpp
test-conda-cpp-valgrind
test-cuda-cpp-ubuntu-20.04-cuda-11.2.2
test-cuda-cpp-ubuntu-22.04-cuda-11.7.1
test-debian-12-cpp-amd64
test-debian-12-cpp-i386
test-fedora-39-cpp
test-r-arrow-backwards-compatibility
test-r-clang-sanitizer
test-r-depsource-bundled
test-r-depsource-system
test-r-dev-duckdb
test-r-devdocs
test-r-extra-packages
test-r-gcc-11
test-r-gcc-12
test-r-install-local
test-r-install-local-minsizerel
test-r-linux-as-cran
test-r-linux-rchk
test-r-linux-valgrind
test-r-macos-as-cran
test-r-minimal-build
test-r-offline-maximal
test-r-offline-minimal
test-r-rhub-debian-gcc-devel-lto-latest
test-r-rhub-debian-gcc-release-custom-ccache
test-r-rhub-ubuntu-release-latest
test-r-rocker-r-ver-latest
test-r-rstudio-r-base-4.1-opensuse155
test-r-rstudio-r-base-4.2-focal
test-r-ubuntu-22.04
test-r-versions
test-ubuntu-20.04-cpp
test-ubuntu-20.04-cpp-bundled
test-ubuntu-22.04-cpp
test-ubuntu-22.04-cpp-20
test-ubuntu-22.04-cpp-emscripten
test-ubuntu-22.04-cpp-no-threading
test-ubuntu-24.04-cpp
test-ubuntu-24.04-cpp-bundled-offline
test-ubuntu-24.04-cpp-gcc-13-bundled
test-ubuntu-24.04-cpp-gcc-14
test-ubuntu-24.04-cpp-minimal-with-formats
test-ubuntu-24.04-cpp-thread-sanitizer
test-ubuntu-r-sanitizer
ubuntu-focal-amd64
ubuntu-focal-arm64
ubuntu-jammy-amd64
ubuntu-jammy-arm64
ubuntu-noble-amd64
ubuntu-noble-arm64
wheel-macos-monterey-cp310-cp310-amd64
wheel-macos-monterey-cp310-cp310-arm64
wheel-macos-monterey-cp311-cp311-amd64
wheel-macos-monterey-cp311-cp311-arm64
wheel-macos-monterey-cp312-cp312-amd64
wheel-macos-monterey-cp312-cp312-arm64
wheel-macos-monterey-cp313-cp313-amd64
wheel-macos-monterey-cp313-cp313-arm64
wheel-macos-monterey-cp313-cp313t-amd64
wheel-macos-monterey-cp313-cp313t-arm64
wheel-macos-monterey-cp39-cp39-amd64
wheel-macos-monterey-cp39-cp39-arm64
wheel-manylinux-2-28-cp310-cp310-amd64
wheel-manylinux-2-28-cp310-cp310-arm64
wheel-manylinux-2-28-cp311-cp311-amd64
wheel-manylinux-2-28-cp311-cp311-arm64
wheel-manylinux-2-28-cp312-cp312-amd64
wheel-manylinux-2-28-cp312-cp312-arm64
wheel-manylinux-2-28-cp313-cp313-amd64
wheel-manylinux-2-28-cp313-cp313-arm64
wheel-manylinux-2-28-cp313-cp313t-amd64
wheel-manylinux-2-28-cp313-cp313t-arm64
wheel-manylinux-2-28-cp39-cp39-amd64
wheel-manylinux-2-28-cp39-cp39-arm64
wheel-manylinux-2014-cp310-cp310-amd64
wheel-manylinux-2014-cp310-cp310-arm64
wheel-manylinux-2014-cp311-cp311-amd64
wheel-manylinux-2014-cp311-cp311-arm64
wheel-manylinux-2014-cp312-cp312-amd64
wheel-manylinux-2014-cp312-cp312-arm64
wheel-manylinux-2014-cp313-cp313-amd64
wheel-manylinux-2014-cp313-cp313-arm64
wheel-manylinux-2014-cp313-cp313t-amd64
wheel-manylinux-2014-cp313-cp313t-arm64
wheel-manylinux-2014-cp39-cp39-amd64
wheel-manylinux-2014-cp39-cp39-arm64
wheel-windows-cp310-amd64
wheel-windows-cp311-amd64
wheel-windows-cp312-amd64
wheel-windows-cp313-amd64
wheel-windows-cp39-amd64

[kou]

@github-actions crossbow submit test-fedora-39-cpp

[github-actions]

Revision: f9b0cf8

Submitted crossbow builds: ursacomputing/crossbow @ actions-5795158c71

Task	Status
test-fedora-39-cpp

[kou]

I'll merge this.