By Jonathan Saul LONDON (Reuters) – Shipping companies remain in the dark over a new international navy coalition being assembled by the United States to combat attacks in the Red Sea, with many vessels continuing to avoid the area or cancelling contracts, sources said on Wednesday. The sources, who include shipping and maritime security officials, say few practical details are known about the initiative launched on Tuesday by Washington or whether it will directly engage in the event of further armed attacks at sea. Iran-backed Houthi militants in Yemen have since Nov. 19 stepped up attacks o…