Nine months after scooping up 150 doctors from Beth Israel Deaconess Medical Center's physician group, fast-growing Steward Health Care System has lured away more than 110 other healthcare providers affiliated with the giant Partners HealthCare System. Hawthorn Medical Associates, the largest multi-specialty practice in the New Bedford area, disclosed Wednesday that it has signed a 10-year affiliation deal with Steward, a Boston-based chain of 11 hospitals and other medical care facilities across Eastern Massachusetts. The agreement takes effect Jan 1. At the end of this year, Hawthorn will let its 14-year affiliation with Partners Community Healthcare, the chain's physician network, expire.