[quant] Add default symmetric qat qconfig for qnnpack (#74507)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74507
* This is the default symmetric qat qconfigs for qnnpack.
* Support for symmetric quantization is not available from other backends.
* Observers are similar to symmetric PTQ qconfigs for qnnpack.
Reviewed By: jerryzh168
Differential Revision: D34804808
fbshipit-source-id: 22c11b89242a98f54029ac195f7b984e42809164
(cherry picked from commit ea751ded1174ba2c2f061bafc81573faaf248a9a)
