init add of wandb ai writer

[alexge233]

Proposed change(s)

Added a very simplistic class of WandbWritter and an extremely poor unit test, which appears to work (on a test wandb.ai project). The idea is to be able to publish the exact Tensorboard stats on wandb.ai as it allows teams, projects and collaboration across colleagues. This is not a promotion, and I am not affiliated with wandb.ai in any way.

Useful links (Github issues, JIRA tickets, ML-Agents forum threads etc.)

NA

Types of change(s)

• Bug fix
• New feature
• Code refactor
• Breaking change
• Documentation update
• Other (please describe)

Checklist

• Added tests that prove my fix is effective or that my feature works
• Updated the changelog (if applicable)
• Updated the documentation (if applicable)
• Updated the migration guide (if applicable)

Other comments

Just testing the waters with WandB.ai writter; unit tests probably could do with a lot more work. I was told by Jason Rupert & Miguel Alonso to use the plugin system; so I'm unsure as to whether I was supposed to hack into the stats_writer.py or not. Feel free to reject the PR, but please provide guidance so I can finalise this to an acceptable level.

[CLAassistant]

All committers have signed the CLA.

[visuallization]

@alexge233 Is there any update on this? Would be cool to have wandb support in unity ml agents