Fitness instructor Donna Travers (left) leads a bridal boot camp class at Yolandas in Waltham. Bootcamps are the latest fitness craze for that most motivated of recruits: a woman about to don a wedding gown in front of friends, family, and a dreaded photographer. Embarking on a diet or workout plan is not uncommon among the newly betrothed, but now gyms and trainers are now offering intense, military-style group classes for brides-to-be.