[rllib] parallel pettingzoo import

[rodrigodelazcano]

Why are these changes needed?

This PR includes the ParallelPettingZoo wrapper in the imports of the rllib env module.

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[jkterry1]

@richard4912 Could this please be merged? It's annoying me

[richardliaw]

Hey @jkterry1, sorry about that, I didn't get this notification (also don't forget to tag "richardliaw" not "richard4912").

Thanks!