Add Cohere2 model (#35224)

docs/source/en/model_doc/cohere2.md

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+# Cohere
+
+## Usage tips
+The model and tokenizer can be loaded via:
+
+```python
+# pip install transformers
+from transformers import AutoTokenizer, AutoModelForCausalLM
+
+model_id = "CohereForAI/c4ai-command-r7b-12-2024"
+tokenizer = AutoTokenizer.from_pretrained(model_id)
+model = AutoModelForCausalLM.from_pretrained(model_id)
+
+# Format message with the command-r chat template
+messages = [{"role": "user", "content": "Hello, how are you?"}]
+input_ids = tokenizer.apply_chat_template(messages, tokenize=True, add_generation_prompt=True, return_tensors="pt")
+
+gen_tokens = model.generate(
+    input_ids,
+    max_new_tokens=100,
+    do_sample=True,
+    temperature=0.3,
+    )
+
+gen_text = tokenizer.decode(gen_tokens[0])
+print(gen_text)
+```
+
+## Cohere2Config
+
+[[autodoc]] Cohere2Config
+
+## Cohere2Model
+
+[[autodoc]] Cohere2Model
+    - forward
+
+
+## Cohere2ForCausalLM
+
+[[autodoc]] Cohere2ForCausalLM
+    - forward
+
+