RL: Add chips_per_vm hyperparameter and fix an issue of missing config

[charlesli640]

Description

Fix b/471046638
Fix an issue of missing config in types.py

Tests

Follow the tutorial doc to run Reinforcement Learning on single-host TPUs. Need this change to make it working.

Checklist

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[A9isha]

Thanks Charles!