U.S. Physician Group Market Size, Share, Opportunities, And Trends By Number of Physician (2 to 10, 11 to 24, 25 to 50, More than 50), By Ownership (Physician-Owned, Hospital-Owned, Others), By Specialty (Primary Care, Pediatrics, OB/GYN, Ophthalmology, Orthopedics, Psychiatry, Cardiology, Dermatology, Others), And By Payor (Public Health Insurance, Private Health Insurance/Out-of-pocket), Forecasts From 2023 To 2028