LONDON (Reuters) - 1/BRUMP-TREXIT HAZE Things may be coming to a head in British and U.S. politics. Details emerging over President Donald Trump's interaction with Ukraine's leader could add more grist to impeachment proceedings against him. The last time a president was impeached - Bill Clinton in 1998 - it took 2-1/2 months between proceedings being brought and the eventual House vote to impeach him. So there's likely plenty more noise ahead.The other question is what UK Prime Minister Boris..