Members of the Cambridge City Council appointed longtime deputy city manager Richard Rossi Monday to the city’s top spot next year. The council voted 8 to 1 to promote Rossi to the city manager post once it is vacated by Robert Healy, who is retiring June 30 after 32 years on the job. Rossi, 66, who grew up in Cambridge and now lives in Watertown, promised hard work and good communication to the council on Monday. “I’m just so happy with this opportunity,” Rossi said. “This is a dream come true for me.”