Is your feature request related to a problem? Please describe.
The current Nvidia integration comprises a NvidiaTextEmbedder, NvidiaDocumentEmbedder, NvidiaRanker andNvidiaGenerator but no NvidiaChatGenerator.
We should implement a NvidiaChatGenerator component and add a code example to https://haystack.deepset.ai/integrations/nvidia

Describe the solution you'd like
nvidia/src/haystack_integrations/utils/nvidia/nim_backend.py contains a generate method that uses the /chat/completions endpoint.
We should implement a chat_generate in nim_backend.py. After that generate can probably be refactored to call chat_generate with a list containing a single ChatMessage where the "role" is set to "user".

Note that we are implementing a run_async in all ChatGenerators too. An initial implementation of NvidiaChatGenerator without run_async would be okay but better if we add it too. #1379

Describe alternatives you've considered

Additional context
Adding this component was suggested on discord.