Provide Out-of-the-Box Integration for a Popular Templating Framework

ADK includes a minimal templating mechanism for the `LlmAgent#instruction` field. To avoid imposing a specific dependency, it uses the `InstructionProvider` interface, allowing developers to integrate their preferred templating framework.

However, this flexibility requires developers to create their own integrations for popular frameworks, leading to duplicated effort. To improve the developer experience, we should offer official, out-of-the-box support for widely-used templating engines.

This issue tracks the creation of the first community-driven integration with a popular framework.

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Potential use cases to support:

* https://github.com/google/adk-python/issues/575

Start with the LlmAgent#instruction field and the InstructionProvider interface described in the issue, then review the linked use case at google/adk-python#575. The framework to support is not selected; done means an official integration with a popular templating framework that avoids duplicated developer effort.

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