[rollout] fix: Add LoRA datatype based on rollout model type to the LoRA config

[mgilmore-relace]

What does this PR do?

Bug fix for #3654

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[gemini-code-assist]

Code Review

This pull request aims to set the LoRA data type based on the main model's data type in the vLLM rollout worker configuration. This is a necessary fix to ensure consistency. However, the current implementation for resolving the data type is not robust and could lead to runtime errors if certain valid dtype strings (like 'fp16') are used in the configuration. I have provided a suggestion for a more robust and simpler implementation that leverages vLLM's internal dtype handling.

[waleko]

bumping this!