feat: implement comprehensive GreptimeDB cluster health checker

[JefferyChu001]

This commit implements a complete health checking tool for GreptimeDB clusters with the following features:

Core Components

• Metasrv Checker: Validates etcd and PostgreSQL backends with CRUD operations and permission testing
• Frontend Checker: Tests connectivity to metasrv and validates HTTP configuration
• Datanode Checker: Comprehensive S3 and file storage validation with performance benchmarks

[Copilot]

Pull Request Overview

This PR implements a comprehensive health checking tool for GreptimeDB clusters with extensive testing capabilities for etcd/PostgreSQL backends, HTTP/gRPC connectivity validation, and S3/file storage performance benchmarking.

Key changes include:

• Complete metasrv checker with etcd and PostgreSQL CRUD operations and permission testing
• Frontend checker for metasrv connectivity and server configuration validation
• Datanode checker with S3 storage validation and optional performance benchmarks

Reviewed Changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/main.rs	CLI implementation with async support and JSON/human output formats
src/common.rs	Core checking framework with status tracking and result formatting
src/config.rs	Configuration parsers for all GreptimeDB components
src/error.rs	Comprehensive error handling with categorized error types
src/metasrv.rs	Metasrv checker with etcd/PostgreSQL operations and permission validation
src/frontend.rs	Frontend checker for metasrv connectivity and address parsing
src/datanode.rs	Datanode checker with S3/file storage validation and performance tests
src/tests/mod.rs	Test module declaration with Chinese comment
src/tests/integration_tests.rs	Extensive integration tests covering error scenarios
test-*.toml	Test configurations for different GreptimeDB components
*.example.toml	Example configurations for reference

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