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ARROW-15080: [Python][C++] Enable tuples conversion to interval

Allows tuples to be converted to MonthDayNanoInterval
when type is explicitly specified.

Also, add missing branch for intervals to strategy.py

Closes #12348 from emkornfield/ARROW-15080

Lead-authored-by: emkornfield <emkornfield@gmail.com>
Co-authored-by: Micah Kornfield <micahk@google.com>
Co-authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>