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ARROW-14506: [C++] Conda support for google-cloud-cpp

This PR adds support for `google-cloud-cpp` to the Conda files.
Probably the most difficult change to grok is the change to compile with
C++17 when using Conda:

- Conda defaults all its builds to C++17,
  [this bug](https://github.com/conda/conda-build/issues/3375) goes into
  some detail as to why.
- Arrow defaults to C++11 if no `CMAKE_CXX_STANDARD` argument is
  provided.
- Abseil's ABI changes when used from C++11 vs. C++17, see
  https://github.com/abseil/abseil-cpp/issues/696
- Therefore, one must compile with C++17 to use Abseil in Conda.
- And because `google-cloud-cpp` has a direct dependency on Abseil,
  exposed through the headers, one must use C++17 to use
  `google-cloud-cpp` too.

Closes #11916 from coryan/ARROW-14506-add-google-cloud-cpp-to-conda-files

Lead-authored-by: Uwe L. Korn <uwe.korn@quantco.com>
Co-authored-by: Carlos O'Ryan <coryan@google.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>