chore: update CHANGELOG for v7.0.0

Author: taeold

CHANGELOG.md

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+- BREAKING: Drop support for Node.js 16. Minimum supported version is now Node.js 18. (#1747)
+- BREAKING: Remove deprecated `functions.config()` API. Use `params` module for environment variables instead. (#1748)
+- BREAKING: Upgrade to TypeScript v5 and target ES2022. (#1746)
+- BREAKING: Unhandled errors in async `onRequest` handlers in the Emulator now return a 500 error immediately. (#1755)
+- Add support for ESM (ECMAScript Modules) alongside CommonJS. (#1750)
+- Add `onMutationExecuted()` trigger for Firebase Data Connect. (#1727)