By Uditha Jayasinghe and Alasdair Pal COLOMBO (Reuters) -Sri Lanka’s main opposition party joined anti-government protesters on Friday in rejecting the appointment of a new prime minister and insisted the president resign to take responsibility for the country’s disastrous economic crisis. President Gotabaya Rajapaksa appointed five-time prime minister Ranil Wickremesinghe to his sixth term late on Thursday, but opposition comments signalled it was not likely to resolve the political and economic disarray in the strategic Indian Ocean island nation. A week of violent clashes between protesters…