Add sigmoid operator to Arm backend (#4114)

Summary:
Implemented node visitor, annotator, and test
TOSA  MI and BI passes, U55 BI fails on compilation.

Change-Id: I229f3ceb8b2edeccdc23003be8aefe20f327d835

Pull Request resolved: https://github.com/pytorch/executorch/pull/4114

Reviewed By: kirklandsign

Differential Revision: D60094551

Pulled By: digantdesai

fbshipit-source-id: 156ff48f92f6046c24ef05332c21ef38d9af0d59