feat: store metadata using JSON in SQLDocumentStore

[masci]

Related Issues

• fixes Metadata values are being dropped when list of values are provided #3434

Proposed Changes:

• Use a JSON marshaller to store metadata values
• Remove the validator so we don't drop unsupported data types anymore
• Emit a warning when passing filters to query() as they won't work as expected if metadata have compound data types

How did you test it?

Existing tests

Notes for the reviewer

• I am not sure about the warning on query() as it can get verbose, but I also don't want users to have the false perception the SQLDocumentStore fully supports lists metadata.

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 tests that demonstrate the correct behavior of the change
• I've used the conventional commit convention for my PR title
• I documented my code
• I ran pre-commit hooks and fixed any issue

[masci]

@anakin87 FYI as you implemented the validator and provided a lot of feedback in the original discussion

[anakin87]

@masci thanks.
It seems a good step forward 💫

[anakin87]

If validation is removed, these lines

haystack/haystack/document_stores/sql.py

Lines 403 to 408 in 9539a20

	meta_orms = []
	for key, value in meta_fields.items():
	try:
	meta_orms.append(MetaDocumentORM(name=key, value=value))
	except TypeError as ex:
	logger.error("Document %s - %s", doc.id, ex)

can be reverted to:

haystack/haystack/document_stores/sql.py

Line 389 in 54518ac

meta_orms = [MetaDocumentORM(name=key, value=value) for key, value in meta_fields.items()]

[ZanSara]

LGTM 👍

I'm happy with the warning being verbose, it should be clear that this is partial support and that it will be quirky. Let's tackle it in the next step.