Add a stdlib logging.Filter recipe in recipes/

[jieyao-MilestoneHub]

What

Add a recipes/logging_filter.py example showing a stdlib logging.Filter that runs redact_args over every log record's args and extra payload before emission.

Expected outcome

• New file recipes/logging_filter.py (under 60 lines)
• A RedactionFilter(logging.Filter) subclass with a filter(self, record) method that:
  • If record.args is a Mapping, walks it through redact_args
  • If record.__dict__ contains user-injected extra keys, walks those through redact_args too
  • Returns True (the filter only mutates, never drops)
• A 10-line usage snippet at the bottom showing logger.addFilter(RedactionFilter())
• README "Three killer examples" gets a bullet linking to this recipe (or add a "Recipes" section)

Why this is good for newcomers

• Pure stdlib, no extra deps
• The filter is small but production-useful
• Pattern translates directly to OTel attribute redaction (a future recipe)

Pointers

• Source: src/redactkit/core.py — redact_args is the only API needed
• See CONTRIBUTING.md for dev setup

[hemal9102]

Hi, I'd like to work on this issue. Could you assign it to me?