JOHANNESBURG — South Africa’s intelligence services are investigating who was behind a chartered plane that landed in Johannesburg with more than 150 Palestinians from war-ravaged Gaza who did not have proper travel documents and were held onboard on the tarmac for around 12 hours as a result, the country’s president said Friday. The plane landed Thursday morning at O.R. Tambo International Airport, but passengers were not allowed to disembark until late that night after immigration interviews