Add mild domain randomization to Car Racing Env

[jjshoots]

Description

This adds a mild domain randomization trait to the Car Racing Env.

Simply pass domain_randomize=True, and the road and background colours will be randomized.

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Before

After

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[pseudo-rnd-thoughts]

Could you add a test for hardcore=True?

Edit:
There don't appear to be any tests for lunar lander hardcore=True.
It may make sense to make a test file for all of the box2d, classical control and toy text environment kwargs. Currently, there isn't one

[jjshoots]

Yea I couldn't find any tests for CarRacing, and I agree with you that there should be. I'll get to implementing one then. Though it remains an interesting question what should be tested. In the lunar lander case, it could be tested because there was already a heuristic algorithm that could solve the environment. There doesn't seem to be one for car racing.

[RedTachyon]

Overall looks good, just left one nitpicky comment for code quality

Actually, one thought. Would it make sense to name this something else than hardcore? I know there are some envs that already follow this naming pattern, but it's extraordinarily undescriptive.

Also - we might want to register an extra env to make it easier to create this version, something like "CarRacingHardcore" or whatever Hardcore might get renamed to.

[RedTachyon]

Do we have to store the colors with two different representations? (one is 0-1, the other is 0-255)

[jjshoots]

Gotcha, fixed it

[RedTachyon]

I guess v0 can be labelled as the original version; v1 will come live with 0.24.0 at the earliest, so probably better to put that (seeing as 0.23.1 is already out)

[jjshoots]

Gotcha, fixed it

[jjshoots]

@RedTachyon I've changed hardcore to domain_randomize, hopefully that's more descriptive, also registered it.