Hyperparameter Optimization Module

[middleyuan]

The pull request contains

1. DDPG, SAC, PPO

• Change the saving method for the checkpoint.
• Add activation as an argument for the constructor.

2. GPMPC

• Add the feature that allows one to learn GP in parallel (this speeds up roughly D times faster, where D is the dimension of the dynamics)
• Add activation as an argument for the constructor ('Matern' or 'RBF' kernel are supported).

3. Hyperparameter optimization (HPO) module

• database.py implements the functions that interact with MySQL.
• hpo_sampler.py defines the hyperparameter spaces for the selected controller.
• hpo.py defines the hyperparameter optimization class.

4. safe_control_gym/hyperparameters/README.md describes the basic steps for running HPO.

[adamhall]

Run precommit hooks etc. to ensure formatting is good.

[adamhall]

experiments folder was removed. Clean up experiments and move to examples folder that exists in the current main branch.

[adamhall]

Move any files used for tests into the tests directory.

[adamhall]

rename hyperparameters_13.....yaml to something more readable.