Implement Help menu in super sidebar navigation

What does this MR do and why?

This creates the "❔ Help" menu in the super sidebar. Resolves #385748 (closed).

Screenshots or screen recordings

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:

3. The super sidebar should now appear on every page.
4. The Help menu is on the bottom-left.

Validate

1. Please double-check that all the links work.
2. Pay extra attention to the last two menu items that open a modal/drawer. Open and close both of them multiple times. There initially was a bug around that behaviour.

MR acceptance checklist

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