docs: administration: document input rate metrics and rate gate

[eschabell]

Add the rate_window and rate_gate settings shared by all input plugins to the pipeline section, covering the pause and resume thresholds and how backpressure scales the effective limit. Add the five new fluentbit_input_rate_* metrics to the monitoring reference.

Note: this update needed to cover code changes without doc PR

Summary by CodeRabbit

• Documentation
  • Added guidance for monitoring input ingestion rates and rate-limiting behavior.
  • Documented new Prometheus metrics for byte rate, record rate, busy chunks, limiting status, and retry attempts.
  • Included configuration options, defaults, threshold behavior, backpressure handling, and an HTTP input example.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: e6920db4-1c04-42e2-bddf-d01fe4ff27bd

📥 Commits

Reviewing files that changed from the base of the PR and between 6d81f90 and 047e6d3.

📒 Files selected for processing (2)

• administration/configuring-fluent-bit/yaml/pipeline-section.md
• administration/monitoring.md

📝 Walkthrough

Walkthrough

The documentation now covers per-input ingestion-rate metrics, optional rate limiting, rate-gate behavior, and five V2 Prometheus metrics.

Changes

Input rate documentation

Layer / File(s)	Summary
Rate metrics and rate-gate documentation administration/configuring-fluent-bit/yaml/pipeline-section.md, administration/monitoring.md	Documents ingestion-rate measurement, rate limits, backpressure adjustment, pause and resume thresholds, rate-gate states, related Prometheus metrics, and an HTTP configuration example.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• fluent/fluent-bit-docs#2546: Updates related configuration documentation for HTTP ingress queue settings.
• fluent/fluent-bit-docs#2566: Documents another group of V2 Prometheus metrics.

Suggested labels: 5.0.4

Suggested reviewers: patrick-stephens, lecaros

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the documentation changes for input rate metrics and the rate gate.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Create PR with unit tests

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[eschabell]

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Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@administration/configuring-fluent-bit/yaml/pipeline-section.md`:
- Line 99: Update the gate behavior description to explain the combined-limit
semantics: pausing occurs when either the byte-rate or record-rate limit is
exceeded, and resumption requires both measured rates to fall below their
respective effective limits multiplied by rate_gate.resume_ratio.
- Line 97: Update the rate gate activation wording near the rate_gate
configuration description to state that rate_gate must be enabled and at least
one of rate_gate.max_bytes or rate_gate.max_records must be set to a non-zero
value; preserve that zero means unlimited.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: be8a90a6-52e4-4804-8bd1-619b83cdca10

📥 Commits

Reviewing files that changed from the base of the PR and between 0eb06a6 and 6d81f90.

📒 Files selected for processing (2)

• administration/configuring-fluent-bit/yaml/pipeline-section.md
• administration/monitoring.md

[eschabell]

@patrick-stephens ready for review!