chore: Deprecate legacy filter

[vblagoje]

Why:

This update aims to encourage users to transition to a new filter syntax by introducing a deprecation warning for the old syntax. This preemptive measure ensures a smoother transition before the old syntax is removed in an upcoming release, thereby maintaining code compatibility and reducing future technical debt.

What:

• Added an import statement for the warnings module in filters.py.
• Inserted a DeprecationWarning in the convert function indicating the use of deprecated filter syntax.

How can it be used:

• Deprecation Warning: When the convert function is called with the old filter syntax, a warning message will inform users about the deprecation, encouraging them to update their code.

How did you test it:

• Added a deprecation warning which inherently doesn't disrupt functionality.

Notes for the reviewer:

• Verify that the deprecation warning appropriately triggers when old syntax is used.
• Ensure the message is clear and directs users to the documentation for the new syntax.

[coveralls]

Pull Request Test Coverage Report for Build 9853471364

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.003%) to 90.019%

---

Files with Coverage Reduction	New Missed Lines	%
utils/filters.py	2	98.65%

Totals
Change from base Build 9853347868:	0.003%
Covered Lines:	6782
Relevant Lines:	7534

---

💛 - Coveralls

[davidsbatista]

nit: we could link to the doc/api with the new syntax

[davidsbatista]

LGTM - just a small suggestion

[vblagoje]

@dfokina do we have a page already where we describe the new filters?

[dfokina]

@vblagoje Are these the old filters? https://docs.haystack.deepset.ai/docs/metadata-filtering and if so, what changed?

[vblagoje]

@vblagoje Are these the old filters? https://docs.haystack.deepset.ai/docs/metadata-filtering and if so, what changed?

No these are the new ones, thanks @dfokina 🙏

[vblagoje]

@dfokina while at it do we have a policy (practice) to link to docs page from warnings arising in source code? I'm not finding such instances in the code....

[davidsbatista]

@vblagoje I also don't know if it's a policy, it was just a nit/suggestion

[vblagoje]

@vblagoje I also don't know if it's a policy, it was just a nit/suggestion

Right I agree, no problem, it is important to be consistent in these warnings, that's why I wanted to ask @dfokina so we know for the future.

[vblagoje]

Ah this PR is outdated now with #8004
@shadeMe I'll mark #8004 with 2.3.0 milestone, cool?

[dfokina]

@vblagoje I personally think it's useful to link to current docs from these warnings, but let's see case-by-case where it makes sense, and then make it a policy, if it's useful everywhere :)