Set ensure_ascii=False in JSON dump within apply_chat_template
Author: junrae6454
Pull request: yes

# What does this PR do?

* This PR modifies the apply_chat_template function to improve handling of non-ASCII characters in JSON output by setting ensure_ascii to False. This change ensures that characters such as "안녕?" and emojis are correctly rendered in their original form rather than as escaped sequences.
* Modified the ImmutableSandboxedEnvironment in apply_chat_template to set ensure_ascii=False in jinja_env.policies['json.dumps_kwargs'].

Before
```python
try:
    import jinja2
    from jinja2.exceptions import TemplateError
    from jinja2.sandbox import ImmutableSandboxedEnvironment
except ImportError:
    raise ImportError("apply_chat_template requires jinja2 to be installed.")

def raise_exception(message):
    raise TemplateError(message)

jinja_env = ImmutableSandboxedEnvironment(trim_blocks=True, lstrip_blocks=True)
jinja_env.globals["raise_exception"] = raise_exception
template = jinja_env.from_string("{{tools|tojson}}")
template.render(tools={"안녕?":"🤗"})
```

```python
>>> '{"\\uc548\\ub155?": "\\ud83e\\udd17"}'
```

After
```python
try:
    import jinja2
    from jinja2.exceptions import TemplateError
    from jinja2.sandbox import ImmutableSandboxedEnvironment
except ImportError:
    raise ImportError("apply_chat_template requires jinja2 to be installed.")

def raise_exception(message):
    raise TemplateError(message)

jinja_env = ImmutableSandboxedEnvironment(trim_blocks=True, lstrip_blocks=True)
jinja_env.globals["raise_exception"] = raise_exception
jinja_env.policies['json.dumps_kwargs']['ensure_ascii'] = False
template = jinja_env.from_string("{{tools|tojson}}")
template.render(tools={"안녕?":"🤗"})
```

```python
>>> '{"안녕?": "🤗"}'
```


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Comments:
Hey, very cool that there are more than just me using `tojson`, but it's a duplicate of #31041 :)

Hi @junrae6454, thank you for this PR! As mentioned, this is a duplicate of the earlier PR #31041, so I'm going to close it, but we appreciate the contribution, and feel free to add any comments or suggestions on that PR!