Boston officials are holding interviews tomorrow with firms interested in launching a planning study of City Hall and City Hall Plaza — part of Mayor Martin J. Walsh’s vision to re-imagine a more inviting space on the bleak concrete landscape.A selection committee of city and Boston Redevelopment Authority employees plans to spend tomorrow interviewing four firms — Stantec Architecture & Engineering, Utile Inc., Sasaki Associates and Machado & Silvetti Architecture — pitching to lead the study and master plan, said Walsh spokeswoman Laura Oggeri.