Add offline fallback

[aliciapaz]

Description

Provide a customized offline experience for users, i.e. an offline page.

Cache scripts and assets to improve performance and load styles in offline fallback.

How has this been tested?

Manual testing was performed in the following platforms:

• Safari and Chrome on Desktop (Mac)
• Chrome on Android
• Safari on iOS

To test locally

On desktop:

Run the local server and open the browser, then:
Option 1: shut the server down and refresh the page or try to navigate.
Option 2: use the DevTools' "offline" throttling mode (screenshot).

On mobile

Use Ngrok and simulate a lost connection with airplane mode.

• Manual testing
• System tests
• Unit tests
• None

Checklist

• CI pipeline is passing
• My code follows the conventions of this project
• I have performed a self-review of my code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• I have added seed data to the database (if applicable)

Screenshots/Loom