Update chat_template.json to incorporate `generation` tag

Incorporating `generation` tag to chat_template.json so that `return_assistant_tokens_mask` can work correctly with the tokenizer (https://github.com/huggingface/transformers/pull/30650/files). A self-contained test script is pasted below.

```python
from transformers import AutoProcessor

processor = AutoProcessor.from_pretrained("llava-hf/llava-interleave-qwen-0.5b-hf")

# Define a chat histiry and use `apply_chat_template` to get correctly formatted prompt
# Each value in "content" has to be a list of dicts with types ("text", "image")
conversation = [
{
"role": "system",
"content": [
{"type": "text", "text": "You are a helpful assistant."},
]
},
{
"role": "user",
"content": [
{"type": "text", "text": "What is shown in this image?"},
{"type": "image"},
],
},
{
"role": "assistant",
"content": [
{"type": "text", "text": "This is a picture of a cat."},
]
},
{
"role": "user",
"content": [
{"type": "text", "text": "What is the cat doing?"},
]
},
{
"role": "assistant",
"content": [
{"type": "text", "text": "The cat is sleeping on a sofa. It looks very comfortable."},
]
}
]

template = (
"{% for message in messages %}"
"{{'<|im_start|>' + message['role'] + '\n'}}"
"{# Render all images first #}"
"{% for content in message['content'] | selectattr('type', 'equalto', 'image') %}"
"{{ '<image>' }}"
"{% endfor %}"
"{# Render all text next #}"
"{% if message['role'] != 'assistant' %}"
"{% for content in message['content'] | selectattr('type', 'equalto', 'text') %}"
"{{ '\n' + content['text'] }}"
"{% endfor %}"
"{% else %}"
"{% for content in message['content'] | selectattr('type', 'equalto', 'text') %}"
"{% generation %}"
"{{ '\n' + content['text'] }}"
"{% endgeneration %}"
"{% endfor %}"
"{% endif %}"
"{{'<|im_end|>' + '\n'}}"
"{% endfor %}"
"{% if add_generation_prompt %}"
"{{ '<|im_start|>assistant\n' }}"
"{% endif %}"
)
print("\n")
print(repr(template))
print("\n")

prompt = processor.apply_chat_template(
conversation,
chat_template=template,
add_generation_prompt=False,
tokenize=False
)
print(prompt)

inputs = processor.apply_chat_template(
conversation,
chat_template=template,
add_generation_prompt=False,
tokenize=True,
return_assistant_tokens_mask=True,
return_dict=True
)
print(inputs['assistant_masks'])
```

chat_template.json

@@ -1,3 +1,3 @@
 {
-  "chat_template": "{% for message in messages %}{{'<|im_start|>' + message['role'] + '\n'}}{# Render all images first #}{% for content in message['content'] | selectattr('type', 'equalto', 'image') %}{{ '<image>' }}{% endfor %}{# Render all text next #}{% for content in message['content'] | selectattr('type', 'equalto', 'text') %}{{ '\n' + content['text'] }}{% endfor %}{{'<|im_end|>' + '\n'}}{% endfor %}{% if add_generation_prompt %}{{ '<|im_start|>assistant\n' }}{% endif %}"
+  "chat_template": "{% for message in messages %}{{'<|im_start|>' + message['role'] + '\n'}}{# Render all images first #}{% for content in message['content'] | selectattr('type', 'equalto', 'image') %}{{ '<image>' }}{% endfor %}{# Render all text next #}{% if message['role'] != 'assistant' %}{% for content in message['content'] | selectattr('type', 'equalto', 'text') %}{{ '\n' + content['text'] }}{% endfor %}{% else %}{% for content in message['content'] | selectattr('type', 'equalto', 'text') %}{% generation %}{{ '\n' + content['text'] }}{% endgeneration %}{% endfor %}{% endif %}{{'<|im_end|>' + '\n'}}{% endfor %}{% if add_generation_prompt %}{{ '<|im_start|>assistant\n' }}{% endif %}"
 }