llama : add chat template for RWKV-World + fix EOT (#9968)

* Add chat template for RWKV-World

Signed-off-by: Molly Sophia <mollysophia379@gmail.com>

* RWKV: Fix the chat template not being used

Signed-off-by: Molly Sophia <mollysophia379@gmail.com>

* RWKV v6: Set EOT token to ``\n\n``

Signed-off-by: Molly Sophia <mollysophia379@gmail.com>

* readme: add rwkv into supported model list

Signed-off-by: Molly Sophia <mollysophia379@gmail.com>

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Signed-off-by: Molly Sophia <mollysophia379@gmail.com>