feat: Add XLSXToDocument converter

[sjrl]

Related Issues

• fixes https://github.com/deepset-ai/haystack-private/issues/87

Proposed Changes:

Draft of the Excel to Document converter

How did you test it?

Added tests

Notes for the reviewer

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

[sjrl]

Hey @bglearning I'd like to discuss with you how got references to work (e.g. pointing to the correct row in the original Excel table) to make sure we accommodate that properly in this component.

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Details

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• Overall coverage increased (+0.07%) to 90.762%

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Totals
Change from base Build 12414372846:	0.07%
Covered Lines:	8430
Relevant Lines:	9288

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💛 - Coveralls

[bglearning]

btw @sjrl , looks like to_csv actually also supports list of strings.

header: bool or list of str, default True

So the out_header (or equivalent) can be made the same for both (List[str]) which would just be the columns by default (if excel_column_names is optional).

Also on the flip side, to_markdown is eventually calling the tabulate library which uses the headers kwarg

- `headers` can be an explicit list of column headers
- if `headers="firstrow"`, then the first row of data is used
- if `headers="keys"`, then dictionary keys or column indices are used

[sjrl]

Just realized I'd like to do a bit more testing. Especially what happens when a complicated table is converted such as what happens if cells are merged, etc.

So a TODO

• Add test with realistic table (ie like one from a client)

[anakin87]

I have some initial comments.
Overall, the PR looks good.

[anakin87]

Thanks.

Feel free to add a test with a realistic table (#8522 (comment)), then it's ready to go.