pipeline: filters: lookup added new filter page

[olegmukhin]

New filter documentation page outlines description, example configuration and CSV handling for the new LookUp filter to be implemented as part #fluent/fluent-bit/pull/10620.

Summary by CodeRabbit

• Documentation
  • Added comprehensive Lookup filter documentation and navigation entry: configuration options with defaults; examples in multiple config formats; sample input/output; metrics (processed/matched/skipped); behavior notes on case sensitivity, header handling, quotes, whitespace trimming, multiline records and data-type handling; clarification that the lookup table is loaded at startup.

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[coderabbitai[bot]]

Walkthrough

Adds comprehensive documentation for a new Lookup filter: configuration fields (data_source, lookup_key, result_key, ignore_case, skip_header_row), examples (Fluent Bit YAML and config), sample input/output, CSV matching rules, metrics, and operational notes; also updates the docs SUMMARY/TOC.

Changes

Cohort / File(s)	Summary
Lookup filter documentation pipeline/filters/lookup.md	Added full documentation: configuration fields with defaults, behavior (CSV loaded at startup, first column = key, second = value), case/quote/whitespace handling, skip_header_row, metrics (processed/matched/skipped), and examples (Fluent Bit YAML and Fluent Bit config) with sample input→output.
TOC / Summary entry SUMMARY.md	Added "Lookup" entry under Filters in the documentation SUMMARY/TOC.

Sequence Diagram(s)

(The changes are documentation-only; no control-flow or runtime behavior changes to diagram.)

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

• Verify documentation accurately reflects implemented filter behavior (CSV parsing, key/value rules).
• Confirm examples (YAML and Fluent Bit config) and sample I/O align with actual behavior.
• Check SUMMARY.md entry placement and formatting.

Poem

🐇 I nibble rows of CSV bright,
First column sings, the next takes flight.
A hop, a match, a value found,
Docs tucked soft beneath the ground.
Read along — the lookup's sound.

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding a new documentation page for the Lookup filter to the pipeline filters section.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

🧪 Generate unit tests (beta)

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between dab162178d4682f3e7daaf426829c7f1eb7392ab and 5600eddaa391668ff10d9713b303946ac0e8052e.

📒 Files selected for processing (1)

• pipeline/filters/lookup.md (1 hunks)

🚧 Files skipped from review as they are similar to previous changes (1)

• pipeline/filters/lookup.md

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