feat: support victoria metrics push exporter

[Hardikl]

No description provided.

[Copilot]

Pull Request Overview

This PR introduces support for VictoriaMetrics as a new exporter type by implementing a push-based exporter that sends metrics to VictoriaMetrics' Prometheus-compatible endpoint. The implementation refactors common Prometheus rendering utilities into a shared package to be reused by both Prometheus and VictoriaMetrics exporters.

Key changes:

• Implements a new VictoriaMetrics exporter with URL/address-based configuration and HTTP client for pushing metrics
• Refactors Prometheus-specific histogram and escaping utilities into a shared exporters package
• Updates validation and configuration to recognize VictoriaMetrics as a valid exporter type

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cmd/exporters/victoriametrics/victoriametrics.go	Implements the VictoriaMetrics exporter with Init, Export, Emit, and Render methods
cmd/exporters/victoriametrics/victoriametrics_test.go	Adds test coverage for VictoriaMetrics configuration options and rendering
cmd/exporters/utils.go	Extracts shared histogram and escaping utilities from Prometheus exporter
cmd/exporters/prometheus/prometheus.go	Refactors to use shared utilities from exporters package
cmd/exporters/prometheus/prometheus_test.go	Updates tests to use shared utilities
cmd/poller/poller.go	Adds VictoriaMetrics case to exporter loading logic
cmd/tools/doctor/doctor.go	Adds VictoriaMetrics to valid exporter types
cmd/tools/doctor/testdata/testConfig.yml	Adds test configurations for VictoriaMetrics
pkg/tree/tree_test.go	Updates expected exporter count from 13 to 17

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