feat: Make Prometheus gRPC histogram buckets configurable

[kevinjom]

Add support for custom histogram buckets for gRPC request latency metrics via PROMETHEUS_GRPC_HISTOGRAM_BUCKETS environment variable.

Summary by CodeRabbit

• New Features
  • Added support for customizing Prometheus gRPC histogram buckets to provide fine-tuned observability metrics collection. Users can now specify custom bucket threshold values (comma-separated seconds) via a new environment variable. When this variable is not configured, the system automatically applies sensible default histogram buckets for standard usage scenarios and typical workloads.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR adds support for custom Prometheus gRPC histogram buckets. A new configuration field PrometheusGRPCHistogramBuckets is introduced to the Config struct, populated from an environment variable. The initialization logic is updated to apply these custom buckets when provided, or fall back to default buckets when empty.

Changes

Cohort / File(s)	Summary
Configuration Enhancement config/config.go	Added new public field PrometheusGRPCHistogramBuckets []float64 with environment variable binding and documentation for comma-separated histogram bucket values in seconds.
Histogram Initialization core.go	Updated gRPC histogram setup to conditionally apply custom buckets from config when non-empty, otherwise use default buckets.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 A config field hops into place,
Custom buckets now keep the pace,
Prometheus metrics, tuned just right,
Histograms gleam with buckets so bright! 📊

🚥 Pre-merge checks | ✅ 3

✅ 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 and concisely summarizes the main change: making Prometheus gRPC histogram buckets configurable, which matches the core functionality added across config and core files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch feat/configurable-grpc-prom

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[Copilot]

Pull request overview

Adds an opt-in configuration for Prometheus gRPC handling-time histogram bucket boundaries, allowing operators to tune latency distributions via an environment variable while preserving the library defaults when unset.

Changes:

• Added PROMETHEUS_GRPC_HISTOGRAM_BUCKETS config field ([]float64) to supply custom bucket thresholds (seconds).
• Updated Prometheus gRPC histogram initialization to apply custom buckets when configured, otherwise fall back to go-grpc-prometheus defaults.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
core.go	Conditionally enables gRPC handling-time histograms with custom bucket boundaries when configured.
config/config.go	Introduces a new config field and documentation comment for supplying histogram buckets via env var.

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[Copilot]

config/README.md is gomarkdoc-generated from config/config.go and currently doesn’t include the newly added PrometheusGRPCHistogramBuckets field. Please regenerate/update the generated docs so the public configuration documentation matches the code.