Season the chicken thighs on both sides with salt and pepper. Heat the oil in a large skillet over medium high heat and brown the chicken thighs for several minutes on each side.
Place the thighs in the slow cooker along with the onions, celery, carrots, and garlic. Pour in the chicken stock and water, cover, and cook on low for 6-8 hours.
Carefully remove the chicken thighs and place on a cutting board. Add the egg noodles, sage, thyme and parsley to the slow cooker and turn the heat on high for 9-10 minutes.
While the noodles are cooking, use two forks to gently shred the chicken. Once the noodles are cooked, return the chicken to the slow cooker. Stir in the cream (if using), lemon juice, salt and pepper.
Leftover soup that is chilled may look broken once fat from the soup separates from the cream. Simply reheat the soup, stir, and it will come back together. Boneless, skinless chicken breasts my be substituted for a leaner soup.