SNOW-2306184: config refactor - Release Notes

Author: sfc-gh-mraba

RELEASE-NOTES.md

@@ -15,6 +15,7 @@
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 # Unreleased version
 ## Backward incompatibility
+* **Configuration System (NG)**: File-based configuration sources (`snowsql_config`, `cli_config_toml`, `connections_toml`) now use **connection-level replacement** instead of field-level merging. When a later file source defines a connection, it completely replaces the entire connection from earlier file sources - fields are NOT inherited. Environment variables and CLI arguments continue to overlay per-field on top of the file-derived connection. This provides more predictable configuration behavior where file-defined connections are atomic units.
 
 ## Deprecations