By Humeyra Pamuk WASHINGTON (Reuters) – Little known are the names of the Americans detained abroad despite their years’ long plight to regain their freedom, but now, thanks to a work of art unveiled on Wednesday in the U.S. capital, the faces of more than a dozen U.S. citizens held by foreign governments will be visible to tens of thousands. A mural displaying the faces of 18 Americans detained overseas, including U.S. basketball star Brittney Griner who has been held in Russia since February on drug charges, has been installed on the side of a building in a narrow alley in the Georgetown nei…