[Docs] Add reinforcement learning example illustrating gpu-to-gpu RDT and GRPO. (#57961)

## Description
Example for first blog in the RDT series using NIXL for GPU-GPU tensor
transfers.

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Signed-off-by: Ricardo Decal <[email protected]>
Signed-off-by: Stephanie Wang <[email protected]>
Co-authored-by: Ricardo Decal <[email protected]>
Co-authored-by: Stephanie Wang <[email protected]>
Co-authored-by: Qiaolin Yu <[email protected]>

Author: 4 people