*Goal:*
The Optimizer class (similar to the model) aims to consilidate different optimizer initializations we support with some base user arguments to determine the optimizer as well as an optional name argument for a user to explicitly choose their optimizer.

https://github.com/instructlab/training/pull/456

*Acceptance Criteria:*
Optimizer class is introduced to the library which allows users to create an object that represents one of the optimizer classes we support. a user should be able to use this object to run training.