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ARROW-15789: [C++] Update OpenTelemetry to v1.2.0

Quickly bump the version since it changes a few APIs we'll use (most notably for #11920).

#11963 will also need updating, but the conda-forge packages need to be updated first.

This does not include the fix needed for #12408, that will require another version bump.

Closes #12516 from lidavidm/arrow-15789

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>