feat(group_theory/subgroup/basic): Analog of `mul_aut.conj` for normal subgroups. (#9552)
feat(group_theory/subgroup/basic): Analog of `mul_aut.conj` for normal subgroups. (#9552)

Analog of `mul_aut.conj` for normal subgroups (pretty much just copying the code from `data/equiv/mul_add_aut.lean`).



Co-authored-by: tb65536 <25c750517795e47f172dc8c552ed72c7de260bd4@users.noreply.github.com>

leanprover-community/mathlib,leanprover-community/mathlib