Add CHANGELOG.md entry

Author: d10c

extensions/ql-vscode/CHANGELOG.md

@@ -7,6 +7,7 @@
 - Increase the required version of VS Code to 1.82.0. [#2877](https://github.com/github/vscode-codeql/pull/2877)
 - Fix a bug where the query server was restarted twice after configuration changes. [#2884](https://github.com/github/vscode-codeql/pull/2884).
 - Add support for the `telemetry.telemetryLevel` setting. For more information, see the [telemetry documentation](https://codeql.github.com/docs/codeql-for-visual-studio-code/about-telemetry-in-codeql-for-visual-studio-code). [#2824](https://github.com/github/vscode-codeql/pull/2824).
+- Add a "CodeQL: Trim Cache" command that clears the evaluation cache of a database except for predicates annotated with the `cached` keyword. Its purpose is to get accurate performance measurements when tuning the final stage of a query, like a data-flow configuration. This is equivalent to the `codeql database cleanup --mode=normal` CLI command. In contrast, the existing "CodeQL: Clear Cache" command clears the entire cache.
 
 ## 1.9.1 - 29 September 2023