When the Select field has a default value, it automatically signs with
it. If you change it, you need to refresh the page to re-sign again with
that value. This PR improves the UX by making the default value
"selectable" in the dropdown menu.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- Updated the `DropdownField` component to simplify the handling of
default values, ensuring the dropdown starts without a pre-selected
option.
- Improved the clarity of the placeholder text in the dropdown,
enhancing user experience.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
