SNOW-2306184: config-ng refactor

[sfc-gh-mraba]

Pre-review checklist

• I've confirmed that instructions included in README.md are still correct after my changes in the codebase.
• I've added or updated automated unit tests to verify correctness of my new code.
• I've added or updated integration tests to verify correctness of my new code.
• I've confirmed that my changes are working by executing CLI's commands manually on MacOS.
• I've confirmed that my changes are working by executing CLI's commands manually on Windows.
• I've confirmed that my changes are up-to-date with the target branch.
• I've described my changes in the release notes.
• I've described my changes in the section below.
• I've described my changes in the documentation.

Changes description

This PR introduces the Next Generation (NG) Configuration System - a complete rewrite of Snowflake CLI's configuration resolution mechanism that addresses critical issues in the legacy system.

What's New

Core Improvements:

• Explicit 7-level precedence stack with predictable, deterministic ordering
• Two-phase resolution model: File sources use connection-level replacement; overlay sources (env vars, CLI args) use field-level merging
• Complete resolution history tracking for debugging configuration issues
• Extensible architecture with clean abstractions for adding new configuration sources
• Immutable, read-only sources - all configuration discovery is side-effect free

Key Benefits:

• Debug exactly where each config value comes from using: snow helpers show-config-sources --verbose
• Predictable precedence - consistent behavior across all configuration sources
• Better troubleshooting with resolution chains and history export
• Backward compatible via feature flag

How to Enable

Enable via environment variable:

export SNOWFLAKE_CLI_FEATURES_ALTERNATIVE_CONFIG_PROVIDER=true

Verify it's active:

snow helpers show-config-sources

Configuration Behavior

File-based sources use connection-level replacement (same as legacy system):

• When connections.toml defines a connection, it completely replaces that connection from earlier files (e.g., ~/.snowsql/config)
• Fields are NOT inherited between files
• Environment variables and CLI arguments merge at the field level

This maintains the same behavior as the legacy system while providing better visibility into the resolution process.