[Accessibility] Header component improvements

Problem/Motivation

Some aria attributes are used incorrectly.
Incorrect semantics of the main menu list.

Steps to reproduce

Go to the site.
Open the `inspector elements` on the browser.
Check the `aria` and `role` attributes on the header HTML structure.

Proposed resolution

Add correct `aria` and `'role` attributes and improve HTML structure.

Remaining tasks

N/A

User interface changes

The header component has a semantic HTML structure using correct `aria` and `role` attributes.

API changes

N/A

Data model changes

N/A