Add GSA privacy policy link to page footers

[danswick]

As part of our ongoing compliance work, we learned we're not meeting the "system use notification" requirement. Per a 🔒 recent announcement, we should be able to satisfy the requirement by linking to GSA's website privacy policy page.

### Tasks
- [x] Add privacy policy link to FAC app footer.
- [x] Add privacy policy link to FAC static site footer.

As a reminder, this cannot be published to the static site or app until the code freeze is over.

[Leighdiddy]

new guidance on website warning banners.pdf

Here is some extra context from a recent GSA-wide email!

[phildominguez-gsa]

This was completed for the app here, which closed this ticket