Limits and colimits indexed by preorders

In this file, we obtain the following very basic results about limits and colimits indexed by a preordered type J:

• a least element in J implies the existence of all limits indexed by J
• a greatest element in J implies the existence of all colimits indexed by J

instance Preorder.instHasLimitsOfShape (C : Type u) [CategoryTheory.Category.{v, u} C] (J : Type w) [Preorder J] [OrderBot J] : CategoryTheory.Limits.HasLimitsOfShape J C

instance Preorder.instHasColimitsOfShape (C : Type u) [CategoryTheory.Category.{v, u} C] (J : Type w) [Preorder J] [OrderTop J] : CategoryTheory.Limits.HasColimitsOfShape J C