Generously spray your slow cooker. Add in the rinsed wild rice and boneless skinless chicken breasts.In a sauce pan over medium heat, add in all the cut vegetables (carrots, celery, onions) with the olive oil. Sautee for 4-5 minutes and then transfer to the slow cooker.Add in the frozen corn, thyme, sage, chicken bouillon, and chicken broth.Cover and cook on high for 3-4 hours or low for 7-8 hours. Remove the lid, shred the chicken, and return the lid.In a saucepan over medium heat, melt the butter. Briskly whisk in the flour until a thick dough-like substance has formed.Slowly add in the milk a little bit at a time until a thick cream sauce is formed. Allow to simmer on low heat for about 10 minutes and then add to the slow cooker.Stir everything together well. Adjust seasonings to taste preference, add salt and pepper, and adjust creaminess level by adding more milk if desired.Serve while hot.