feat: add default template to DynamicPromptBuilder

[tstadel]

Related Issues

Currently we cannot have both:

• a default prompt template defined (PromptBuilder)
• dynamically change prompt templates at runtime (DynamicPromptBuilder)

There are two options:

• A we extend DynamicPromptBuilder and leave PromptBuilder as is
• B we extend PromptBuilder and deprecate DynamicPromptBuilder

This is Option A
See #7655 for Option B

Proposed Changes:

This extends DynamicPromptBuilder to have a default prompt template that is specified at init time.

default_template = "This is the default prompt: \\n Query: {{query}}"
prompt_builder = DynamicPromptBuilder(runtime_variables=["query"], template=default_template)

pipe = Pipeline()
pipe.add_component("prompt_builder", prompt_builder)

# using the default prompt
result = pipe.run(
    data={
        "prompt_builder": {
            "query": "Where does the speaker live?",
        },
    }
)
#  "This is the default prompt: \n Query: Where does the speaker live?"

# using the dynamic prompt
result = pipe.run(
    data={
        "prompt_builder": {
            "template": "This is the dynamic prompt:\\n Query: {{query}}",
            "query": "Where does the speaker live?",
        },
    }
)
#  "This is the dynamic prompt: \n Query: Where does the speaker live?"

How did you test it?

• added tests

Notes for the reviewer

• There is a breaking change: prompt_source param has been renamed to template for consistency. We can undo that if necessary.
• Given that PromptBuilder only has a subset of DynamicPromptBuilder's and no additional functionality, I would prefer Option B
• A Chat counterpart to DynamicPromptBuilder would still need to be implemented

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 8968331832

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.002%) to 90.331%

---

Files with Coverage Reduction	New Missed Lines	%
components/builders/dynamic_prompt_builder.py	1	97.44%

Totals
Change from base Build 8938725904:	-0.002%
Covered Lines:	6521
Relevant Lines:	7219

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💛 - Coveralls

[tstadel]

We decided to go forward with #7655