Site Header improvements

[maany]

Description

Improvements to the Site Header component and the Page

• The menu items need to be reorganized i.e. split into items and sub-items.
• The switch-account feature needs to be connected to the list items in the active accounts section
• The get-site-header feature should be connected to get the list of available accounts and the currently active account
• The logout feature should be connected to the logout button

Motivation

No response

Change

No response

Additional Information

• The Rucio API needs to be changed.

[maany]

Fixed in #409