Add Jinja2TimeExtension to ChatPromptBuilder

[bilgeyucel]

Is your feature request related to a problem? Please describe.
In the PromptBuilder, we use the Jinja2TimeExtension if it is available to allow users to inject the current date into the prompt. The same should be possible for the ChatPromptBuilder.

Describe the solution you'd like

• Add extension to ChatPromptBuilder
• documentation

[bilgeyucel]

I'll implement this feature to add Jinja2TimeExtension to ChatPromptBuilder, following the same pattern used in PromptBuilder. Here's my proposed implementation:

# In chat_prompt_builder.py, update the imports:
from haystack import component, default_from_dict, default_to_dict, logging
from haystack.dataclasses.chat_message import ChatMessage, ChatRole, TextContent
from haystack.utils import Jinja2TimeExtension  # Add this import

# Then in the __init__ method, update the environment initialization:
try:
    # The Jinja2TimeExtension needs an optional dependency to be installed.
    # If it's not available we can do without it and use the ChatPromptBuilder as is.
    self._env = SandboxedEnvironment(extensions=[Jinja2TimeExtension])
except ImportError:
    self._env = SandboxedEnvironment()

This will enable the use of the {% now %} tag in ChatPromptBuilder templates, which allows users to inject the current date/time into their prompts. For example:

from haystack.dataclasses import ChatMessage
from haystack.components.builders import ChatPromptBuilder

# Create a template with the date/time tag
template = [
    ChatMessage.from_system("Today's date is {% now 'UTC' %}"),
    ChatMessage.from_user("Write a summary about {{topic}}")
]

# Create the ChatPromptBuilder with the template
builder = ChatPromptBuilder(template=template)

# Run the builder with a topic
result = builder.run(topic="Artificial Intelligence")

This will produce a prompt with the current date injected into the system message.

Would you like me to also update the docstring to include examples of using the time extension?