Improve user dropdown experience

What does this MR do and why?

1. It closes the user dropdown when the status update modal is open - before it just stayed behind the modal overlay
2. It fixes the issue when the status update modal is initiated twice (by the header.js and super_sidebar_bundle.js when the super_sidebar_nav FF is enabled). I'm not sure whether this issue was here initially or something had changed but I've noticed it when fixing addressign the 1st item, so decided to fix it here as well given it is a tiny change

How to set up and validate locally

Prepare

1. Enable the feature flag:

echo "Feature.enable(:super_sidebar_nav)" | rails c

2. Enable the user setting from the user dropdown:

4. The super sidebar should now appear on every page.
5. Open the user menu and click set/edit status.
6. Make sure that the dropdown is closed once the modal shows up
7. Make sure that only one modal is shown - after closing the firts one, their shoudl be no other behind it)

Related to #396872 (closed)