Add ClickhouseBackup Plugin Support

[jitendra1411]

Overview

This PR introduces a new Backup plugin architecture to the ClickHouse Operator, enabling automated backup operations via an external plugin service. Issue: #1795

---

Current PR Includes

1. Operator Enhancements

• CRDs

  • ClickhouseBackup (CHB) — manage one-time backup requests with S3 configuration, whitelist/blacklist filtering, and method/plugin settings.

• Controller Updates

  • Operator reconciles CHB/CHSB CRs and communicates with a gRPC backup plugin using JSON-serialized request data.
  • Adds plugin discovery via CR labels/annotations.
  • Implements lifecycle management and status reporting.

2. Go Plugin Skeleton

• Introduces a gRPC interface for backup operations using BackupRequest and BackupResult messages.
• Plugin architecture allows future extension for operations like restore, encryption, incremental backups, etc.

---

Motivation & Benefits

• Modular Design: Backup behavior is decoupled from the operator — update, replace, or extend the plugin without touching core operator logic.
• Extensibility: Support for diverse backup implementations (e.g., S3, local disk, incremental, etc.).
• Production-Ready: Enables defined workflows for both one-off and scheduled backups, ensuring reliable defense against data loss.

---

TODO

• Restore Workflow: Implement a corresponding restore service via plugin.
• Test Cases: Implement the test cases
• ClickhouseScheduledBackup (CHSB) Implement code for scheduled backup
• Generic gRPC Client: Implement a reusable gRPC client inside the operator for communication with different plugins.

---

Testing Notes

• Validate CHB and CHSB workflows manually using a mock plugin server.
• Status updates should reflect backup success or failure states.
• Scheduling logic (cron parsing, suspension, etc.) requires validation.

[manishrawat1992]

Will this get accepted.

[discostur]

Would be really cool to see this getting merged