feat(catgory_theory/sites): Image sheaf (#15282)
feat(catgory_theory/sites): Image sheaf (#15282)



Co-authored-by: Andrew Yang <5a6b17dbbc661dec6b250b080ab0033de7d56af5@users.noreply.github.com>

leanprover-community/mathlib,leanprover-community/mathlib