feat: Implement RAGEvaluationHarness and related classes

[shadeMe]

Proposed Changes:

This PR implements the RAGEvaluationHarness and its related classes, building up on #4, #5.

Part of deepset-ai/haystack#7526.

How did you test it?

Unit tests

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

[shadeMe]

The test failure is due to a seemingly missing dependency, but the logs show that it's being installed 🤔 I'll look into this later, but the PR is reviewable. Tests pass locally.

[davidsbatista]

Good work Madeesh, I left some minor comments, otherwise looks good.

[davidsbatista]

This is exactly like the function above, only changing the input_mapping={"query": "query"} for the RAGExpectedComponent.QUERY_PROCESSOR - maybe we can make this one function and make this an arg or some other way to collapse this into a single function?

RAGExpectedComponent.QUERY_PROCESSOR: RAGExpectedComponentMetadata(
                name="retriever", input_mapping={"query": "query"}
            )

[shadeMe]

The motivation behind having separate "default" functions is to make it as simple as possible for the user to initialize a pipeline without having to understand the mapping of the expected components. If we were to merge the two into a single function, we'd have to expose some kind of enumeration to select the type of query processor component (as it can't be a simple boolean flag given the semantics of the parameter), which introduces more code than it removes.

[coveralls]

Pull Request Test Coverage Report for Build 9349272889

Details

• 324 of 336 (96.43%) changed or added relevant lines in 8 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+4.1%) to 97.764%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
test/evaluation/harness/rag/test_harness.py	151	153	98.69%
haystack_experimental/evaluation/harness/rag/harness.py	113	123	91.87%

Totals
Change from base Build 9193174995:	4.1%
Covered Lines:	612
Relevant Lines:	626

---

💛 - Coveralls

[silvanocerza]

Looks good. 👍