Optimize Privacy Center /fides.js download with cache headers and a local public/assets/fides.js file

[NevilleS]

Description

In #3105 we refactored the Privacy Center to serve a custom bundle of the fides.js Javascript package, initialized with the tenant-specific configuration sourced from the Privacy Center backend. This works swimmingly, but needs some optimization before it's ready for production use.

Acceptance Criteria

• Add reasonable cache headers to the /api/fides-js route to ensure both browsers and CDNs will cache the result
• During the privacy-center build, copy the generic fides.js package to /public/assets/fides.js
• Test that this "virtual" file is properly cached by browsers and CDNs

[Roger-Ethyca]

moving to done.