[a11y] Update footer designs to address additions like vulnerability disclosure

[reitermb]

Description:

Follow-on from #1979 — delivers modification to the footer so that all links are housed in a single list element as opposed to multiple (per column).

AC:

• [ ] Footer appears the same visually
• [ ] All links in footer are housed in one list element
• [ ] Testing Checklist has been run and all tests pass
• [ ] README is updated, if necessary

Tasks:

• [ ] Consolidate links into one list element
• [ ] Adjust style attributes to adjust any visual changes

[lhuxraft]

@reitermb To be further refined into a low priority dev ticket (HTML implementation)