Add EXECUTORCH_ENABLE_LOGGING and EXECUTORCH_ENABLE_PROGRAM_VERIFICATION (#638)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/638

Pull Request resolved: https://github.com/pytorch/executorch/pull/617

These flags should be off by default in Release mode, but some users may want to enable them.

This sets a convention for future options like this, which should also use `${_default_release_disabled_targets}`.
ghstack-source-id: 202924824
exported-using-ghexport

Reviewed By: digantdesai

Differential Revision: D49925195

fbshipit-source-id: 953888ddbbfa53ca0dd14305aa60233fb93243ee