Add config to TensorBoard text summary

[vincentpierre]

Motivation and Context

After running a lot of experiments, it can be hard to keep track of the config associated with each training run on TensorBoard. This change adds a human readable config to the Text section of TensorBoard. (see image bellow)

How Has This Been Tested

Not unit tested. Ran an experiment and made config string was accurate.

Types of changes

• Life improvement

Checklist

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have completed my CLA (see CONTRIBUTING)
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.