[TB] Add support for hparam domain_discrete (#40720)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40720
Add support for populating domain_discrete field in TensorBoard add_hparams API
Test Plan: Unit test test_hparams_domain_discrete
Reviewed By: edward-io
Differential Revision: D22291347
fbshipit-source-id: 78db9f62661c9fe36cd08d563db0e7021c01428d
