Merge pull request #6809 from Shopify/02-02_create_a_new_RELEASE_NOTES/3.90.md_file

create a new RELEASE_NOTES/3.90.md file

Author: phyllis-sy-wu

RELEASE_NOTES/3.90.md

@@ -0,0 +1,8 @@
+## App
+
+- Added CLI support for extensions.supported_features in toml [#6765](https://github.com/Shopify/cli/pull/6765)
+- Enable custom headers in CLI GraphiQL. Users can now set custom headers like Shopify-Search-Query-Debug=1 in the GraphiQL interface to pass debugging headers to the Admin API [#6703](https://github.com/Shopify/cli/pull/6703)
+
+## Theme
+
+- Fix shopify theme dev --theme-editor-sync to avoid deleting files during race conditions, especially when multiple changes come from an external process (e.g., AI coding tools) [#6784](https://github.com/Shopify/cli/pull/6784)