When user selects Multi-Agent for template generation, rl_games was one
of the rl_libraries options, but choosing it will generate no algorithm
template because we don't have any rl_game ma_ppo agent cfg. To reduce
the confusion, I will for now disable rl_games selection regarding
multi-agents, we can enable it again once we have a template for that.


## Type of change

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- Bug fix (non-breaking change which fixes an issue)


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## Checklist

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