feat/refactor: Project Overhaul - Modernization, Robustness and v2-preview

[SckyzO]

Summary

This PR introduces a significant overhaul of the ha_cluster_exporter to bring it up to modern Go standards and improve its production reliability. It focuses on three main pillars: Robustness, Modularity, and Modernization. It also integrates critical bug fixes from pending upstream PRs.

Key Changes

1. Robustness & Reliability

• Execution Timeouts: All external command executions (crm_mon, corosync, etc.) now use context.WithTimeout. This prevents the exporter from hanging indefinitely if a system tool becomes unresponsive. Default timeout is 10s, configurable via --collector.timeout.
• Graceful Failure: The exporter no longer crashes if a collector's binary is missing at startup. It now logs a warning and continues, allowing functional collectors to serve metrics. Failing collectors report a success=0 metric.
• Timezone Fix (PR Fix localtime parsing for config_last_change metric #280): Integrated fix for config_last_change metric parsing. It now correctly uses time.Local instead of forcing UTC, ensuring accurate timestamps in environments with local time settings.

2. Modularity

• Selectable Collectors: Added flags to enable/disable specific collectors (e.g., --no-collector.drbd). This reduces resource usage and noise for clusters only using specific components.
• Full Configuration Support: All new flags, including timeouts and collector toggles, are fully supported in the YAML configuration file.

3. Modernization & Architecture

• Standard Go Layout: Restructured the project into standard cmd/ and internal/ directories following community best practices.
• Go 1.24+: Updated the project to Go 1.24 and toolchain 1.24.11.
• Structured Logging (slog): Migrated from go-kit/log to the standard library log/slog for modern, structured logging. Included a compatibility adapter for the Prometheus exporter-toolkit.
• Standard Errors: Replaced the deprecated pkg/errors dependency with native Go error wrapping (fmt.Errorf with %w).
• Clean CLI: Removed several long-deprecated flags (--address, --port, etc.) to simplify the codebase.

4. Tooling & DX

• Dockerfile: Added a modern multi-stage Dockerfile using Alpine and Go 1.24.11.
• Makefile: Optimized build targets and added make docker, make lint and improved promu integration.
• Unit Tests: Fully updated and stabilized the test suite. Forced UTC in Pacemaker tests to ensure deterministic results across different development machines.

Breaking Changes

• Project structure has changed (internal logic moved to internal/).
• Removed deprecated flags: --address, --port, --log-level, --enable-timestamps.
• Minimum Go version is now 1.24.

[SckyzO]

Hello @stefanotorresi

What do you think of my PR ?