Implement left and right Rees congruences

[james-d-mitchell]

Again the title says something, a prototype is what's already implemented in:

https://github.com/semigroups/Semigroups/blob/d735a9289d7fbdccad733ba200d57e39b75f28f7/gap/congruences/congrees.gd

This issue shouldn't be attempted before #939 because it will require right and left ideals to be passed in.