Navigation updates: main nav, footer & vulnerabilities page

[elzannewentzel]

The Demand Gen team requested updates to the customers dropdown in the main navigation, the footer and links on the Use Cases landing page and the Fixing vulnerabilities page.

Note: please refer to this doc for the requirements.

[zlonko]

This is paused pending discussion in the doc on removals and renamings.

[elzannewentzel]

@zlonko All feedback from Erica is now confirmed in the doc 👍