Trac #24087: Automorphism group of finite abelian groups.

This ticket implements the automorphism group of finite abelian groups.
Methods should include:
- generators
- subgroups
- it is essentially a matrix group so the implementation can reflect
that.
- an action on the elements of the underlying abelian group.
- in gap there is a method `AbelianGroupAutomorphismGroup`. We could
wrap that.

URL: https://trac.sagemath.org/24087
Reported by: sbrandhorst
Ticket author(s): Simon Brandhorst
Reviewer(s): Travis Scrimshaw

src/doc/en/reference/groups/index.rst

@@ -34,6 +34,7 @@ Abelian Groups
 
    sage/groups/abelian_gps/abelian_group
    sage/groups/abelian_gps/abelian_group_gap
+   sage/groups/abelian_gps/abelian_aut
    sage/groups/abelian_gps/values
    sage/groups/abelian_gps/dual_abelian_group
    sage/groups/abelian_gps/element_base